The living body information sensor according to the present invention can be attached to a living body. A light emitting unit emits light to the living body. The light receiving unit receives reflected light from the living body that is included in the light emitted by the light emitting unit to the living body, and outputs a signal according to intensity of the reflected light. A control device generates information about the living body based on the signal from the light receiving unit. The control device controls the light emitting unit to turn on and off in an alternate manner. The control device sets a total of a turn-on time of the light emitting unit in a prescribed time interval to be smaller when the living body information sensor is attached to the living body than when the living body information sensor is not attached to the living body.
