PURPOSE: To detect speed data of a moving body with high accuracy by utilizing the Doppler effect.

CONSTITUTION: A measuring head 1A is set so that a laser light is correctly cast to a moving body 33 as a to-be-measured object. When the moving body 33 shifts in position with respect to an advancing direction, light from the measuring head 1A is partly displaced from the moving body 33. A position of the shifted light is detected by a positioning sensor 34. The detected positional data and a position signal of the measuring head 1A are processed at a control part 30, based on which a uniaxial motor actuator 35 is moved to register the measuring head 1A. A signal from the positioning sensor 34 and a speed signal from the measuring head 1A are operated at the control part 30 as well as the positioning data of the measuring head 1A. As a result, a speed signal, a length signal, etc., are output from the control part.