An optical head (200) usable also for an WORM-type optical disk device includes a diffracting optical system (7, 8) which is located on the optical path of a light beam and which diffracts the light beam so as to produce at least three diffracted light beams, and three light-receiving elements which receive the reflected light beams of the three diffracted light beams from the surface of an optical disk. The diffracting optical system is arranged so as to establish a positional relationship in which the three or more diffracted light beams do not lie on a single straight line in the cross-sectional distribution thereof. Among the three diffracted light beams, one lying at the foremost or rearmost position in the forward rotating direction of the optical disk is employed for generating a focusing servo signal or for reading or writing data, and the remaining two are employed for generating a tracking servo signal.