PURPOSE: To perform the work of high grade by enabling the fine adjustment of the lens system of the sight device which observes the work face of the body to be worked.

CONSTITUTION: A control device 33 controls and stops motors 12, 27 so that the focusing point of a laser beam is coincided with the work face of the body 34 to be worked and the reflecting beam is focused on one point on an imaging face 29 by the 2nd sight lens 22, first, and stores the position thereof. Then, the control device 33 controls the motor 12 so that the focusing point of the laser beam is located at the position slipped by the necessary distance from the work face of the body 34 to be worked. It controls the motor 27 so that the reflecting beam thereof is focused on one a point of the imaging face 29 accordingly, controls the motor 12 and 27 with comparing to the stop position and places a command irradiating the laser beam on the body 34 to be worked in case of the given rotation quantity. Thereafter, the laser beam is oscillated from a laser oscillator 1 and its optical path is changed by a dichroic mirror 4 and after focused by a focusing lens 7 it is irradiated on the work point of the body 34 to be worked to perform the cutting, piercing and trimming and the like.