PURPOSE: To measure a body in three dimensions speedily by scanning a light beam which swivels around a point on a focal plane in an object space and providing a screen corresponding to it.

CONSTITUTION: The light beam l is reflected by a rotary plane mirror MY and travels on a plane ω to form a light spot P on an object surface, but only part of luminous flux form the light spot P which is reflected by the plane mirror MY is incident on an object system L within a range wherein the angle ωis larger than a specific value. When the beam l scans on the plane ω, the mirror image l1 of the beam l swivels in a meridian plane Y around a point Q. Then, when the point Q as the center of rotation of the mirror image l1 is set at coordinates (o, -λ, f1), all of the mirror image l1 at optional time passes one point on the object field side plane of the lens system L. On the other hand, the rotary screen R having a screen surface coincident dynamically with a conjugate line l2 is provided. Consequently, the image point is formed sharply on the screen surface S wherever the light spot P is formed in a three- dimensional measurement range.