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Original, functional beauty enabled by combining materials
— stylish and tough, the slimmest G-STEEL yet*

*Based on a Casio survey as of February 2021.

This watch boasts the G-STEEL line’s trademark exterior construction, which combines the strength of carbon with the quality of metal, but now in the slimmest profile ever. The design offers enhanced texture in the dial and the convenience of smartphone connectivity, accelerating the advance of G-STEEL as a multifunction analogue watch.








Independent bezel for striking metallic texture

The watch features a stainless steel bezel in a sophisticated shape. With painstaking attention to detail, even different facets of the same part are uniquely finished by applying lengthwise, crosswise, or circular hairline and mirror finishes, polishing processes and more. The result is an impressive array of metallic surface textures that captivate the eye from every angle.


Vibrant character, with a multilayer vapour deposition- treated dial Vapour deposition

A power-saving module enables the use of an opaquer dial, and highly chromogenic dial colouration is achieved with multilayer vapour deposition. Vapour deposition is applied to the iconic G-STEEL dial indicator and bridge parts as well as parts of the face design, proving the meticulous care taken through the very last detail.

*Above description applies to the GST-B400AD.

Carbon Core Guard structure, for the slimmest G-STEEL yet

Carbon fibre-reinforced resin is used as the material for the case to ensure shock resistance while reducing weight and delivering the slimmest case in the G-STEEL line, at only 12.9 mm. The newly developed form of the button guards makes it possible to offer generously sized stainless steel buttons even in this extra-slim design.


Carbon Core Guard structure, both strong and light

Offering strength, lightness and excellent weather resistance, a carbon fibre-reinforced resin case protects the module. Additionally, buffering components made of resin mounted between the upper and lower bezels help absorb external shocks.

カーボンコアガード構造 (カーボンモノコックケース)

Newly developed module delivers slimness and energy-savings

Optimised, high-density mounting of the circuit board structure made it possible to slim the module. A substantial reduction in power consumption was also achieved by reducing the number of watch hands to two and adopting a low-power Bluetooth® system. The ability to solar charge with an opaquer dial allowed for a high degree of freedom in dial design.


Metal band with double slide lever for easy band changes

*The GST-B400 uses a single slide lever.
*Image shows the GST-B400AD-1A4.


Super Illuminator
(high-brightness LED light)
for maintaining watch readability
in the dark

*Image shows the GST-B400D-1A.


Solar-powered timekeeping
with Bluetooth® and radio control
for enhanced accuracy
and reliability


Multiple functions, all at your fingertips

Smartphone App

- Time & Place
logPressing a button on the watch records the current time and position on a map within the app. Useful as an activity log.

- Reminder setting
The watch will remind you of up to five upcoming events, which you set within the app.

- Automatic time adjustment (four times a day)
- World time for over 300 cities
- Home time/world time switching
- Timer/alarm setting
- Phone finder


  • Shock-resistant structure
  • 20-bar water resistance
  • Tough Solar (Solar powered)
  • Smartphone Link
  • Hand shift feature
  • World time (38 cities)
  • 1/100-second stopwatch
  • Countdown timer
  • 5 daily alarms
  • Double LED light (Super Illuminator)

Note: Bluetooth® is a registered trademark or trademark of Bluetooth SIG, Inc.

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