PURPOSE: To perform distance measuring precisely and enhance the accuracy in tracing, by determining the normal direction of a model surface on the basis of the measuring value at sampling given by two noncontact distance sensors, and making rotation control of a tracer head in this direction.

CONSTITUTION: Coordinates of each vertex of a minute quadrangle on a model 6 surface are obtained from the measuring values at sampling given by two noncontact distance sensors 5a, 5b, and the normal direction is determined using the coordinates of the three necessary of the four vertices, and in this direction two rotary shafts B1, C1 of a tracer head 4 are controlled. Thereby the measuring optical axes of the distance sensors 5a, 5b are directed always vertically to the model 6 surface, which ensures precise measurement of the distance.