PURPOSE: To roughen accuracy in aligning the tip of a nozzle, to stably allow flow-out of adhesive and also to improve the reliability of adhesion.

CONSTITUTION: The photodetector is provided with a holder l for holding an optical system and also having an opening part, a 1st contact face 11a installed around the opening part and a side face which is formed around the 1st contact surface 11a so that it may be in the direction at 90, or at an obtuse angle, or an acute angle from the contact face and also for guiding light beams to the opening part through the held optical system and a photodetecting sensor 2 having a photodetecting face placed opposite to the opening part and a 2nd contact face 2a which is installed around the photodetecting face and also brought into contact with the 1st contact face 11a, and a recessed part is formed from at least a certain part on the side face of the holder l to over the 1st contact face 11a, and the recessed part is formed so as to be positioned in parallel to a facial direction making the obtuse angle to the 1st contact face 11a.