A semiconductor laser oscillator includes a diode unit configured from a plurality of banks, in which one bank is configured from a plurality of laser diodes connected in series. The diode unit includes a wavelength locking mechanism for locking to a plurality of wavelengths. The semiconductor laser oscillator includes a controller configured to control input currents to the laser diodes of each of the plurality of banks individually in correspondence to a characteristic of a wavelength locking efficiency, and to control an output of the diode unit as a whole to a required output.