1. A motor control method comprising the steps of: measuring a time period from an output of a drive detection signal to a next output of a drive detection signal each time a drive detection signal is outputted from a drive detection device that outputs a drive detection signal each time a driven object is driven by a motor by a specified amount; storing the measurement result at the each time of output of a drive detection signal as a measured cycle each time a drive detection signal is outputted from the drive detection device; calculating a driven velocity of the driven object based on the stored measured cycle; calculating an operation amount of the motor such that the calculated driven velocity is equal to a predetermined target velocity at each calculation timing in a predetermined cycle; and drive-controlling the motor based on the calculation result of the operation amount, wherein it is determined, at the each calculation timing, whether or not the driven object is in a low velocity state where an actual velocity is lower than the target velocity, and when it is determined that the driven object is in the low velocity state, calculation of the driven velocity of the driven object is performed based on a measured value being currently measured at the calculation timing in place of the stored measured cycle.