PURPOSE: To measure the quantity of hydrogen in a hydrogen storing tank accurately regardless of the fluctuation in temperature by using a strain gage and a temperature measuring resistor element having the temperature change characteristic suitable for the pressure-temperature characteristic of hydrogen storage alloy.

CONSTITUTION: A body 10 provided with a diaphragm 14 which is deformed with the pressure in a tank is provided in a hydrogen storing tank 2. A pressure detecting strain gage 15 is provided on the diaphragm 14. A temperature measuring resistor element 18 is further provided in the body 10. The strain gage 15 and the temperature measuring resistor element 18 are provided on the neighboring sides of a Wheatstone bridge 30. When the strain gage 15 and the temperature measuring resistor element 18 having the resistance change characteristic which is suitable for the pressure-temperature characteristic of hydrogen storage alloy are used in this way, the shift of the pressure caused by the temperature change in the tank 2 is corrected in the bridge 30. An output voltage Eo corresponding to the quantity of the hydrogen in the tank is obtained from the bridge 30.