Optical pickup using optical phase plate

A first light and second light of a longer wavelength to an optical head device in which laser light sources are used for shorter wavelengths of DVD and CD-R, and using one of them. An objective lens having a predetermined focal length and the position of the information recording surface of the DVD compatible. The control unit controls the optical path of the optical path of the two lights, the light emitted from a laser light source toward the objective lens, the light directed to the objective lens detection unit from the light emitted. Phase shifting means disposed between the objective lens and an optical path control means for moving the optical path from the objective lens control unit proceeds to the phase of the second light, to reduce the size of the beam spot on the information recording surface of the CD-R is formed .