An experimental extracorporeal shock wave lithotripsy system consisting of a piezoceramic shock wave generator and an ultrasonic imaging apparatus has been made. The generated 500 kHz ultrasound wave converts to the shock wave in the focussing region by nonlinear interaction. The measured peak pressure at the focussing point is 130 MPa and the focussing region, in which pressure is more than half of the peak pressure, is about φ3 mm in width and 13 mm in depth. Model urological stones in water and a human renal stone implanted in the right renal pelvis of a mongrel dog are successfully disintegrated into less than φ3 mm fragments.