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 (45) more than necessary. This invention is a living body stimulator for stimulating a living body through a light irradiation from a light source (43). This stimulator includes a temperature sensor for detecting the temperature of the irradiation surface (45) in contact with the living body； and a brightness control unit (63) for changing and controlling the brightness of the light source (43) such that the temperature of the irradiation surface (45) becomes not higher than 42°C, by receiving a detection output from the temperature sensor. The brightness control unit (63) is capable of extending a period of irradiation from the light source (43) in accordance with a decrease in the brightness thereof, when decreasing such brightness through a control regulation.
