A surgical knife comprising a pump configured to supply fluid to a pressure chamber a piezoelectric element configured to generate a pulsed flow by varying the capacity of the pressure chamber when a drive waveform is applied and a drive control unit configured to control the pump and the piezoelectric element, characterized that wherein when the frequency of the drive waveform is varied, the drive control unit generate a drive waveform that a pause or a voltage application time corresponding to the time during which the volume of the pressure chamber is increased is varied without varied a voltage application time corresponding to the time during which the volume of the pressure chamber is reduced.
