@ There is disclosed a dual-wavelength laser apparatus including a laser emitting a laser beam consisting of two wavelength components, a methane cell for controlling and equalizing gains of the two wavelength components, a cavity length modulator including a piezoelectric element for periodically modulating the cavity length of the laser, and a feedback circuit for controlling the modulation center such that the sum of outputs of the two modulated wavelength components is kept substantially constant. The feedback circuit includes a detector for detecting a laser output, a lock-in amplifier for detecting and amplifying an output from the detector, an integrator for integrating an output from the lock-in amplifier, and a high-voltage amplifier for generating a bias voltage set by the integrator.