A laser diode that emits light of a predetermined wavelength, an optical fiber that propagates the light emitted from the laser diode, and a transmission liquid crystal variable optical attenuator that is arranged on an optical axis of the light between the laser diode and the optical fiber and attenuates light intensity of the light are arranged inside a housing. A coupling lens couples the light emitted from the laser diode to an incidence end of the optical fiber. An isolator prevents return light from the optical fiber side.