PURPOSE: To easily input a three-dimensional picture to a computer by reading positions of picture elements of the reflecting light beams from its two-dimensional picture and inputting the positions to the three-dimensional coordinates of the three-dimensional surface or the surface of the solid body after conversion.

CONSTITUTION: When a solid body 3 is scanned in such a way that an origin O of three-dimensional coordinates is fixed inside the solid body 3 and light beams on a straight line are projected on the radial direction parallel to the XZ-plane by means of a 45°-inclined revolving mirror which successively makes relative movement along the fixed straight line of '0' on Z-axis and a fixed value on X-axis, one sides of plane mirrors 2 and 2' are respectively made coincident the fixed straight line of '0' on X-axis and a fixed value on Z-axis and the inclinations of the mirrors 2 and 2' are adjusted so that the optical beam can reflect in the direction parallel to Z-axis on one sides of the mirrors. Therefore, the optical beam never scans the area where the X-coordinate becomes negative and the terminating ends of the line images of the reflecting light always stay on the YZ-plane. Thus a solid body which is '0' or a positive value on X-coordinate can be scanned over its entire surface. Therefore, a three-dimensional picture can be inputted to a computer easily.