To shorten an establishment time and a stopping time of a motor having a dynamic pressure bearing.

A torque control voltage 20 controls a driving current 30 of a scanner motor which rotates a polygon mirror. It is accelerated by generating normal rotation torque at the time of starting the motor until the rotational frequency 40 of the motor reaches a target rotational frequency (an acceleration period T1). It executes rated operations after the establishment time T2 by the reverse rotation torque (a rated rotation period T3). It executes reverse phase braking by the reverse rotation torque to a prescribed rotational frequency Nlimit before reaching the critical rotational frequency of the dynamic pressure bearing (a reverse phase braking time T5) when the motor is stopped. After that, it is stopped by free run or short brake (a slow-speed braking time T6).