An optical pickup apparatus comprises first, second and third light sources to emit light fluxes of wavelength λ1, λ2 and λ3 for conducting recording and/or reproducing information for first, second and third optical information recording mediums having respective protective substrates of thickness t1, t2 and t3 and a diffractive optical element located on a common optical path for the first, second and third light sources. A converged-light spot is formed on the first optical information recording medium with m-th order diffracted-light ray of the wavelength λ1, on the second optical information recording medium with n-th order diffracted-light ray of the wavelength λ2, and on the third optical information recording medium with k-th order diffracted-light ray of the wavelength λ3 generated by the diffractive optical element respectively, wherein one of m, n and k is different from one of other two numbers.