To surely perform operation for changing field of view of an endoscope by providing a reflexive reflection marker being reflected with directional properties in the projected direction of a projected light in the neighborhood of the apex part of a treating tool and providing a marker position detecting means for detecting the position of the reflexive reflection mark on a monitor screen.

A reflexive reflection marker 19a is provided on a holding member 18a of a treating tool. When a treating part of the treating tool enters in a picture on a screen of a TV monitor 26, the projected light from a scope 7 is irradiates the reflexive reflection marker 19a and the projected light is passed through a cover glass 22 and is launched into glass beads 21 and is reflected in the scope 7 direction with directional properties. A picture information outputted from the TV camera 25 is inputted into a color phase opening and operating circuit 27 to extract the reflexive reflection marker 19a and to calculate the position and it is calculated by a moving direction calculating part 28 that the reflexive reflection marker 19a comes to the center of the screen of the TV monitor if a three-dimensional manipulator is moved to either direction.