The optical level control device independently controls the intensities of two beams having different wavelengths that are emitted from a laser oscillator, and the optical level control device includes a wavelength-dependent wavelength plate and a polarization beam splitter. The wavelength-dependent wavelength plate functions as a half-wave plate with respect to the first light wave and as a full-wave plate with respect to the second light wave. Only the rotation angle of the polarization beam splitter about the optical axis is adjusted to set the intensity of the second light wave transmitted rectilinearly through the polarization beam splitter. The polarization beam splitter is then fixed at the adjusted angle, and the rotation angle of the wavelength plate about the optical axis is adjusted to set the intensity of the first light wave.