Provided is a living body stimulator capable of bringing about a stable treatment effect through a light stimulation without increasing the temperature of an irradiation surface more than necessary. This invention is a living body stimulator for stimulating a living body through a light irradiation from a light source. This stimulator includes a temperature sensor for detecting the temperature of the irradiation surface in contact with the living body and a brightness control unit for changing and controlling the brightness of the light source such that the temperature of the irradiation surface becomes not higher than 42° C., by receiving a detection output from the temperature sensor. The brightness control unit is capable of extending a period of irradiation from the light source in accordance with a decrease in the brightness thereof, when decreasing such brightness through a control regulation.
