To provide an on-vehicle device capable of preventing the fan noise from being felt by an occupant in a vehicle as much as possible by controlling the number of rotation of the fan based on the traveling state of the vehicle and the temperature of on-vehicle equipment.

The on-vehicle device controls the number of rotation of a fan 24 so as to be increased when the internal temperature of a casing of a projector 20 is not lower than the specified upper limit value based on the result of detection of an internal temperature detection unit 21 for detecting the internal temperature of the casing of the projector 20, and controls the rotational speed of the fan 24 so as to be decreased when the internal temperature of the casing of the projector 20 is below a specified lower limit value. When the internal temperature of the casing of the projector 20 is in an adequate temperature range, the number of rotation of the fan 24 is controlled according to the speed of a vehicle, the engine speed, the air volume of an air-conditioner, or the opening/closing state of a window.