PURPOSE: To retain the buoyance almost constant with a gyro case of a liquid compensating for variation in the buoyance due to temperature changes by providing an expensible bag body having gas sealed inside in a float type gyro device.

CONSTITUTION: An expansible bag body 25 such as ring-shaped bellows having a gas 24 such as helium sealed inside is fixed on a gyro ball 3. As the temperature of a liquid 22 rises above the set temperature with the outside temperature changing, the specific gravity of the liquid 22 decreases. But the gas 24 expands to inflate the expansible bag body 25 and the buoyance of the liquid 22 working thereon increases thereby compensating for a drop in the buoyance on the gyro ball 3 with a rise in the temperature.