In the present invention, variations in rotational speed of an ultrasonic motor are suppressed and a constant infusion rate maintained even when the infusion rate is extremely low by shortening a wait period when drive voltage is not output without dependence on the performance of a switching unit. In a control method for an ultrasonic motor (3): a drive signal for generating drive voltage to drive the ultrasonic motor (3) is generated by a drive signal generating unit (504) on the basis of a setting rate signal input from a control unit (51) to the drive signal generating unit (504); the drive signal is output by the drive signal generating unit (504) to a drive voltage generating unit (52) that generates the drive voltage; and during a wait period following an output period in which the drive voltage is output, the drive signal generating unit (504) waits, without generating a drive signal, on the basis of the setting rate signal.
