PURPOSE: To crush calcified thrombi while preventing damaging blood vessels carelessly.

CONSTITUTION: A catheter 21 has a pipe 25 made of a conductor provided around the outer periphery of a wire 22 made of a conductor with an insulating tube 26 intervening therebetween. An insulating ring 27 is also interposed between the head 24 of the wire 22 and the end of the pipe 25. The catheter 21 is inserted into a blood vessel while its end is located near a thrombus. DC high voltage pulses are applied at low frequencies to the wire 22 and the pipe 25 from a DC high voltage pulse source 32, so that a shock wave is generated at the end portion of the catheter 21. The calcified tissue of the thrombus is crushed by the shock wave. The catheter 21 can be narrowed so as to be usable in narrow blood vessels.