To shorten the time until a speed servo becomes stable in a start state and to obtain sufficient stability in a steady state.

In a subtracter 32, a drum FG signal reference period whose number of sampling times given as a reference of a rotation period is one is subtracted from a period of a supplied drum FG signal and a speed error is detected. In a subtracter 34, a drum FG signal reference period whose number of sampling times given as the reference of the rotation period is six is subtracted from the period of the supplied drum FG signal, and the speed error is detected. The speed error is supplied to a comb-like filter 35 and FG unevenness is removed. When the number of revolutions does not reach 80% of an object, the speed error where the number of sampling times amplified by an amplifier 33 is one is supplied to an adder 42. When the number of revolutions reaches 80% of the object, the speed error where the number of sampling times amplified by an amplifier 36 is six is supplied to the adder 42.