To provide a simple, light-weight, low cost and high-performance underwater automatic operation indicator lamp switch which automatically forms an indicator lamp circuit by only being thrown in a field sea area from an airplane and a ship or the like in the emergency of distress and water surface contamination or the like, and can also be used as a personal accessory.

The underwater automatic operation indicator lamp switch has a cartridge (2) filling high-pressure gas in an expansion means (1) and an opening device (3). The opening device has an unmoving part (4) and a displacement part (7) being operated by a spring (6) in the functioning of a water sensor (5), and the unmoving part and the displacement part are individually provided with an unmovable terminal (S1) and a displacement terminal (S2) contacting each other in generating displacement. The unmovable terminal and the displacement terminal are interposed in a circuit (10) of the indicator lamp (9) equipped with a power source (8). When the opening device is immersed in water, the water sensor senses that, the cartridge opens by being operated by the spring, and the high-pressure gas spouts from the cartridge. The unmovable terminal and the displacement terminal contact each other and a current flows to turn on the indicator lamp.