When a rotation start position of a rotation shaft 132 is a middle start position 31a (i.e., when rotation of the rotation shaft 132 is stopped in the middle and the rotation is restarted), target rotational speed (relative target rotational speed) is defined using a relative pattern 31 that uses the middle start position 31a as a reference, without using an absolute pattern 33 that is defined using a normal rotation start position 33a as a reference. Upon detecting that a condition that absolute target rotational speed corresponding to an angular position detected by a rotation sensor 134 is greater than the relative target rotational speed is not satisfied, motor control is switched so that the absolute pattern 33 is used.