An optical head includes the following: a light beam separator (35) that includes substantial interference regions for light that is reflected from an information recording medium and travels in a straight path and ±first-order diffracted light produced by information tracks of the information recording medium, and diffracts each of plural light beams in regions (32a, 32b) of the substantial interference regions, where the amount of light is changed by a change in the relative angle between the information recording medium and the objective lens and by a shift of the objective lens in the radial direction of the information recording medium; a light-receiving element (36a, 36b) for receiving the light beam that is reflected by the information recording medium and separated by the light beam separator (35); and an arithmetic circuit that corrects a value of an electrical signal detected by the light-receiving element (36a, 36b) in accordance with a radial position signal corresponding to the amount of shift of the objective lens in the radial direction of the information recording medium, and detects the relative angle between the information recoding medium and the objective lens.