To adjust parallelism easily, smoothly and accurately.

When a knob member 38 is turned, an adjusting screw portion 35 secured to the knob member 38 turns to displace from the internally threaded portion 27a of a constriction portion 27 in the advancing direction. Consequently, a wedge-shaped fitting member 36 is pushed by a knob member 38 through a washer member 42 and displaced in the advancing direction, and a wedge-shaped fitting member 37 is further pushed by the internally threaded portion 27a through a washer member 43 and displaced in the advancing direction. A fitting groove portion 29 is deformed as the wedge-shaped fitting member 36 moves and an inclination movement portion 28 is deformed to turn about the rotating shaft thus varying the angle against the pressed surface of the distal end face 28a.