PURPOSE: To reduce consumption of electric current for emission of light, and to elongate the life of a battery power source while reducing cost by a method wherein an infrared light emitting device for detecting human body is made luminous only when a toilet is regarded as in use with illuminance therein kept above a specified level.

CONSTITUTION: In a sensing device for toilet that is equipped with a circuit for an infrared light emitting device 1, a circuit for a light receiving device 2, a circuit for a power source 3 and a feed water solenoid valve driving circuit 4 and in which reflected rays from a human body that reflects infrared rays emitted from the light emitting device 1 are detected by the circuit for the light receiving device 2 and load for the feed water solenoid valve is driven thereby, an illuminance sensing circuit 5 is provided. Then, the circuit for the infrared light emitting device 1 is driven when illuminance that is above a specified level is detected.