Liquid is ejected in a pulse-like manner from a nozzle provided at the distal end of a liquid ejection pipe. When the liquid is ejected, moving speed of the nozzle is detected. A driving frequency of a piezoelectric element is increased when the moving speed increase. The driving frequency is reduced when the moving speed decreases. Consequently, it is possible to prevent the number of times the liquid is ejected per unit length from changing according to the moving speed of the nozzle. Therefore, it is possible to excise a biological tissue at stable excision depth.
