PURPOSE: To reduce the size of a tracer head by a method wherein the image of single light is formed as a luminescent spot in at least two spots spaced away from each other on a model surface through the optical system of a projection part, and the luminescent spot image of reflection light at the luminescent spot is formed on a displacement detecting element by means of the optical system of a collecting light detecting part.

CONSTITUTION: Light (laser beam) emitted from a single light source (semiconductor element) 12 forms luminescent spots at least at two spots (a) and (b), spaced away from each other, on a model surface by means of optical systems 13 and 14 of a projection part 8A. Reflection light at the luminescent spot is enlarged by optical systems 17 and 18 of light collecting detecting part 8B. The luminescent spot images are formed on respective displacement detecting elements (CCD image sensors) 19A and 19B, and a displacement amount of a luminescent spot image generated due to the protrusions and recessed parts of a model surface through relative movement of the tracer head or a model is simultaneously outputted. Based on output data, the shape of the model surface and a speed vector are calculated.