To simplify the work for regulating a projected line vertically, and shorten the working time by nipping a laser emitting device by a pair of nipping pieces so that no force in the direction of rotating the laser emitting device is added, and mounting the laser emitting device as the projected line projected from the laser emitting device is kept in vertical state.

A laser emitting device 30 is inserted to the mounting hole 11 of a support body 9 and rotated within the mounting hole 11, whereby the angle is regulated to lay a cylindrical lens 33 in horizontal state. The horizontal state is confirmed by supplying a power to the laser emitting device 30 and confirming whether the projected line projected form the laser emitting device 30 is situated on the vertical line or not. Thereafter, fastening male screws 17 are screwed to the fastening female screws 15 of nipping pieces 14 and fastened. The mounting hole 11 part in the nipping pieces 14 is contracted in diameter to nip and fix the laser emitting device 30. No force is added in the circumferential tangent direction of the laser emitting device 30, the laser emitting device 30 is never rotated when it is nipped, and the cylindrical lens 33 is also kept in the horizontal state.