PURPOSE: To adjust finely the angle of a reflection mirror having high reproducibility with high accuracy by tightening and adjusting an elastically deformable adjusting bolt which is locked and fixed to a part for holding the reflection mirror to adjust the optical axis of a laser beam.

CONSTITUTION: The adjustment of the optical axis of a laser beam is accomplished by adjusting optionally an adjusting bolt 14 so as to change adequately the tightening rate thereof and adjusting freely and easily the angle in the set position of a reflection mirror body 13 while checking the error in the optical axis of the laser beam. The extent of the vertical movement of the reflecting surface 13a of the body 13 in the adjusting position appears as the rate adding the contraction rate of a part 12 for holding the reflection mirror near the point of the bolts 14 to be locked to a fixing member 15 to the difference between the advance rate of the screw by the rotation of the bolt 14 and the elongation rate by the elastic deformation of the bolt 14.