A projector with a light source device; an optical modulator for modulating a light beam irradiated by the light source device; a projection optical device for projecting the light beam modulated by the optical modulator in an enlarged manner; and an exterior casing for housing the light source device, the optical modulator, and the projection optical device, includes: an optical diaphragm disposed on an optical path between the light source device and the optical modulator, the optical diaphragm having a light shield for shielding at least a part of an incident light beam, the optical diaphragm adjusting light quantity of a light beam irradiated by the light source device by moving the light shield into and out of the optical path; a nonvisible light eliminator disposed on the downstream of the optical diaphragm on the optical path, the nonvisible light eliminator reflecting or transmitting a light beam in the nonvisible light region of the light beam irradiated by the light source device to guide the light beam in the nonvisible region out of the optical path; and a nonvisible light detector for receiving the light beam in the nonvisible light region which is guided to be out of the optical path by the nonvisible light eliminator, the nonvisible light detector outputting a light-receiving signal.