PURPOSE: To obtain an optical head which attains a recording/reproduced signal having good quality, by making the diameter of a spot used for information recording different from that for another purpose with respect to the optical head which uses a diffraction grating to form plural spots on an optical recording medium.

CONSTITUTION: The luminous flux from a light source is separated into plural luminous fluxes by a diffraction grating element 1, and they are projected to an optical information recording medium to record and reproduce information. this diffraction grating element 1 has a diffraction grating forming part 3 and a diffraction grating non- forming part 4, and the diffraction grating forming part 3 and the diffraction grating non-forming part 4 are arranged in the optical path from the light source to the recording medium so that they are placed in a luminous flux. Since the luminous flux is made incident on both of the diffraction grating forming part and the diffraction grating non-forming part, the ratio of the synthetized light of the 0th-order diffracted light of the diffraction grating forming part and the transmitted light of the diffraction grating non-forming part to the high-order diffracted light from the diffraction grating forming part is freely set in the shape of the diffraction grating forming part, the area ratio of both parts, etc., are set to prescribed values.