PURPOSE: To suppress the errors in the motion and the angle of the laser beam to a minimum by providing a monitoring means and a converging lens to align both positions of the angle and the azimuth of the laser beam on a rotary hinge of a laser beam emitting device.

CONSTITUTION: A device 10 for alignment is used in aligning both positions of the angle and the motion of the laser beam in rotary hinges 16a, 16b of a laser beam emitting device 12 provided with at least one rotatable laser beam optical system. The device 10 for alignment is provided with the rotary hinges 16a, 16b of the laser beam emitting device 12 along the axis A of the laser beam, and a device chassis 20 to receive the laser beam, and the device chassis 20 is rotatable at the hinges. As for the position of the motion of the laser beam, the hi-converging laser beam is monitored by a monitor 24 relative to the X-Y coordinate system. The direction of the angle of the laser beam can be monitored at the focal position connected to a screen 24 through a converging lens 41. Both errors of the motion and the angle of the laser beam can be determined thereby.