To improve safety and reliability by avoiding any inconvenience that a pressurized fluid fed to a pressure chamber in a movable part is leaked to the outside due to a rupture of the wall surface of the pressure chamber, or a leakage out of a pin hole and so on.

A flexible actuator 2 attached to the tip of a catheter 1 is wrapped by a tube 5 with elasticity, forming an exhausting air space 6 there. When a pressurized fluid is leaked into this air space, it is guided to a leak detector 7 with an exhaust tube 8 and thereby a leakage of this pressurized fluid is detected. When this leakage is detected, any pressurization is stopped, whereby any possible leak of the pressurized fluid into the human body is thus obviated.