The present invention reduces the radiation noise and the degradation of the optical waveform appeared in the output of the laser module. The laser module of the present invention comprises the laser diode, the photodiode, and the resistor, which are mounted on the stem of the laser module. The stem includes four lead terminals, one of which is commonly connected to the laser diode ad the photodiode via the resistor. Therefore, the leak of the modulation current applied to the lead terminal, to which the laser diode and the photodiode are commonly connected, may be reduced.