To effectively utilize condensing energy of a battery by connecting a solenoid to the output side of a booster circuit provided for outputting higher voltage than the voltage of the battery.

A booster circuit part 201 boosts the output voltage 3 V of two AA dry cells to 5 V, and dispatches load to a sensor part 301, a valve driving part 401, and a signal processing part 501. When output voltage of a condenser 117 is brought down lower than 5 V due to power consumption by the valve driving part 401 and the like, partial potential of resistors 215, 217 is brought down so as to make a comparator 211 ON, an oscillation circuit 209 is operated so as to make a transistor 207 ON/OFF, and the output voltage of the condenser 117 is raised. When it reaches 5 V, the comparator 211 is made OFF, the oscillation circuit 209 is stopped so as to make the transistor 207 OFF, and hence the output voltage of the condenser 117 is made not to rise over it. The valve driving part 401 is constituted out of an H-bridge circuit 413 provided with a solenoid 403 and the like driving a plunger.