An ultrasound surgery system includes: a handpiece including an ultrasound transducer that generates ultrasound vibration and a treatment portion to which the ultrasound vibration is transmitted a drive current output section provided in a power supply apparatus to which the handpiece is detachably connected, the drive current output section producing and outputting a drive current for driving the ultrasound transducer a drive frequency output section that detects and outputs a drive frequency for driving the ultrasound transducer with a resonant frequency of the ultrasound transducer and a variable current setting section that variably sets the drive current produced by the drive current output section, based on the drive frequency detected by the drive frequency output section, in order to maintain an amplitude or a vibration velocity of the ultrasound vibration in the treatment portion at a predetermined value.
