To measure highly precisely the distance even to rotating bodies whose surfaces have varying surface properties, e.g. unevenness of color and dispersion of gloss, by controlling the output of laser light beam corresponding to the reflectance of the surface of the rotating body computed in advance by irradiating it with laser beams.

Light beams of constant intensity are radiated from a semiconductor laser 12 by a controlling circuit while a rotating body 30 is rotated. At that time, the rotation angle of the rotating body 30 is measured by a rotation angle sensor 26. A part of the light beam diffused and reflected by the rotary body 30 is received by a light receiving element 16 and then the reflectance factor of the surface of the rotating body is computed by a laser output pattern generating circuit 24 based on the quantity of the light reception of the element 16 and the output of the laser light beam. A laser output pattern corresponding to the rotation angle is determined from the obtained reflectance factor and the detected rotary angle and memorized in a memory element in the circuit 24. The rotating body 30 is irradiated with laser light beam in the determined output pattern and a part of the diffused and reflected light beam is received by the element 16 and the accurate distance to the rotating body 30 can be computed by a computing circuit 18.