PURPOSE: To position a work based on multiple intersections appearing on the work when beams of light sources with three or more different colors are crossed and the work is lifted or lowered.

CONSTITUTION: A light source 1 emits a beam of light 1A with the first color, a light source 2 emits a beam of light 2A with the second color different from the first color, and the beam of light 1A and the beam of light 2A are crossed at an intersection 2B. A light source 3 emits a beam of light 3A with the third color different from the first color, and the beam of light 1A and the beam of light 3A are crossed at an intersection 3B. A work 10 is positioned based on the intersection 2B and intersection 3B appearing on the work 10 when a working table 11 is lifted or lowered.