An optical disk apparatus for reproducing, or recording, information from plural types of information carriers, including: two or more light sources with different wavelengths; converging parts for converging light beams emitted from the light sources on the information carrier; movement parts for moving the converged light beam in a direction substantially perpendicular to the surface of the information carrier; convergence condition detection parts for outputting a signal corresponding to the convergence condition of the light beam on the information carrier; amplitude detection parts for measuring the amplitude of the convergence condition signal; and focus control parts for driving the movement parts in accordance with the convergence condition signal and performing control so that the convergence condition of the light beam on the information carrier becomes substantially constant. Upon start, or restart, the apparatus determines the type of loaded information carrier based on a signal from the amplitude detection parts.