PURPOSE: To perform a wavelength multiplex communication or a coherent communication with one semiconductor laser element sections by providing effective refractive index or/and diffraction grating pitch of resonators of respective unit semiconductor laser to be different ones from those of resonators of other unit semiconductor lasers.

CONSTITUTION: Unit semiconductor laser sections A, B, C of a semiconductor laser element 1 are composed of DFB lasers, and the widths W1, W2, W3 of active layers 4 and the pitches a1, a2, a3 of diffraction gratings 21 are different (W1>W2>W3, a1>a2>a3). As a result, a laser light 20 having a wavelength of 1553nm of the emitting light is radiated from the laser section A having W1=1.5μm, a1=2405, a laser light 20 having a wavelength of 1543nm is irradiated from the laser section B having W2=1.0μm, a2=2400, and a laser light 20 having a wavelength of 1533nm is radiated from the laser section C having W3=0.65μm, a3=2395.