Disclosed is the improvement in a dynamic air pressure bearing in which a rotor is supported at high speed in the non-contact state. In an optical deflector, a stationary shaft is planted at the center portion of a housing. A stator core is disposed on a stud. A magnet yoke is integrated with a sleeve rotated relative to the stationary shaft. The magnet yoke contains an inner magnet and an outer magnet. A rotary polygonal mirror is mounted on a flange fixed on the sleeve by means of a center screw and a mirror cap. The rotary polygonal mirror is rotated at high speed together with the sleeve relative to the stationary shaft, thus constituting a dynamic air pressure bearing between the shaft and the sleeve. The stationary shaft is constituted of a main body and a ring-like bearing member fitted in the main body. The bearing member is formed of a ceramic material and formed with grooves for generating dynamic air pressure. The sleeve is preferably constituted of a main body and a bearing member of ceramic.