PURPOSE: To measure a position or length of an object at non-contact by using a laser beam and a recurrence reflector.

CONSTITUTION: A laser beam from a semiconductor laser element 12 is converged through a lens 13, and reflected on a half-mirror 15. The reflected laser light is reflected on an oscillation mirror 14 swinging at a constant oscillation number by a scanning controller 16, and furthermore made parallel by a parabolic mirror 18. The neighborhood of the upper edge of an object 11 to be measured is scanned. The laser light not shielded by the object 11 advances straight, and is received by a recurrence reflector 19. The laser light not reflected by the reflector 19 is converged by the parabolic mirror 18, reflected on the mirror 14, passed on the the mirror and converged through a lens 20 A light receiving signal of a light receiving element 21 is input to a controller 22. On the other hand, part of the laser light from the laser element 12 is converted into a reference signal by a reference sensor 17 through the mirror 14, and input to the controller 22. The position of the object 11 from the time displacement of the reference signal and the light receiving signal is measured.