Casio is a Japanese electronics maker headquartered in Shibuya, Tokyo. It began as a small workshop, Kashio Seisakujo, opened by Tadao Kashio in 1946. The company, Casio Computer Co., Ltd., was founded in 1957 after Tadao and his three younger brothers completed the 14-A relay calculator. From calculators, Casio expanded into watches. Its first digital watch, the Casiotron QW02, came out in November 1974. The name secondhand watch buyers look for most is G-Shock, the shock-resistant watch first released through the DW-5000C series in 1983. Besides that there are Baby-G, Edifice, Oceanus, and Pro Trek. Watches are now Casio's largest business, about 67 percent of consolidated sales in the fiscal year ending March 2026.
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Tadao Kashio, an engineer with deep knowledge of fabrication technology, founded Kashio Seisakujo in Mitaka, Tokyo, in April 1946. The workshop first took on subcontract work, such as making microscope parts and gears. His three younger brothers, Toshio, Kazuo, and Yukio, later joined him. The first original product was the yubiwa pipe, a ring-shaped cigarette holder invented by Toshio. Its sales helped fund the development of a calculating machine.
In 1949 the brothers saw an electrically powered calculating machine at a business show in Tokyo, and then began building their own. The result, the 14-A calculator, was released in June 1957. Casio Computer Co., Ltd. was formally established on 1 June 1957, with their father, Shigeru Kashio, as its first president. In October 1960 the writing of the name Kashio was changed from kanji to katakana, and that is its Japanese name today.
Casio entered the watch market in November 1974 with the Casiotron QW02, a digital watch with a calendar that adjusts automatically to the length of each month. In the late 1970s and the 1980s, Casio developed calculator watches as well as watches with features such as games, telephone number storage, world time, and environmental sensors.
In 1981 the engineer Kikuo Ibe proposed a watch that could withstand shock. The project used a target called Triple 10: a battery that lasts ten years, water resistance up to 10 bar, and survival of a ten-meter drop. The first G-Shock, the DW-5000C, was released in 1983 and grew into one of Casio's main watch brands.
- G-Shock DW-5000C: the first G-Shock model, released in 1983 with targets of a 10-year battery, 10 bar water resistance, and a 10-meter drop resistance.
- Casiotron QW02: Casio's first digital watch, released in November 1974 with an automatic calendar.
- Baby-G: a line of shock-resistant watches that sits alongside G-Shock.
- Oceanus: Casio's line of metal watches.
- Pro Trek: a line of watches for outdoor activities.
What we check before listing
We start with the model code printed on the back of the case, then match it against the look and functions of the watch. We press every button, and we also test the light, alarm, and stopwatch, because a stuck button or a screen with lines often points to a faulty module. On resin models, we check the strap and bezel for cracks, brittleness, or a sticky surface. On metal models, we look at scratches, impact marks, and the condition of the strap links. We check the crystal, rubber gasket, and the space behind the crystal for condensation or signs of moisture. Water resistance cannot be confirmed by eye alone, so we do not promise it on secondhand watches.
Caring for it
Clean the case and resin strap with a damp cloth or a soft brush and a little soap, then dry it before storing. Avoid solvents and perfume, which can make resin brittle. Replace the battery on time so it does not leak and damage the module. Rubber gaskets age, so if the watch is often exposed to water, have its water resistance checked by a trusted watchmaker.
FAQ
What does Triple 10 mean for the G-Shock?
It was the original target of the G-Shock project: a battery that lasts ten years, water resistance up to 10 bar, and survival of a ten-meter drop. This target applied to the first model, the DW-5000C from 1983. A secondhand watch has aged, so its condition still needs to be checked one watch at a time.
Is a secondhand Casio watch still water resistant?
Not necessarily. Rubber gaskets age over time and impacts can affect how well the case seals. The water resistance marking on the case shows the original specification, not the current condition. It is best not to swim with it before it has been tested.
How do I find out which Casio model I have?
Look at the model code on the back of the case, for example DW-5000C for the first G-Shock. You can use that code to look up the model, its functions, and its original look.
What Casio watch lines are there besides G-Shock?
Casio also makes Baby-G, Edifice, Oceanus, which is made of metal, and Pro Trek for outdoor activities. There are also digital and analog watches sold under the Casio name alone.
References
Facts summarised and rewritten from the sources above (CC BY-SA licence).