A PFO closing device for bringing the septum primum and the septum secundum into contact with each other and joining them together includes a clamping mechanism and energy supplying device. The clamping mechanism includes a needle part for puncturing the septum primum, and a clamping member for cooperating with the needle part in clamping therebetween tissue of the septum primum and the septum secundum. The energy supplying device supplies energy for joining the tissues clamped by the needle part and the clamping member. The clamping mechanism is mounted in a catheter so as to be protrudable from and retractable into the catheter.
