PURPOSE: To measure inclination angle at high speed with high accuracy, by moving a measuring means along a reference axis (X-axis in this execution example), measuring the gap between the moving body to be worked or an electrode and the measuring means in the continued state timely, computing the inclination angle based on this measurement result, and composing it so as to perform the correction.

CONSTITUTION: During the movement of a measuring means 8 by a moving means, the result of the distance between the body 1 to be worked or an electrode and the measuring means 8 being measured in continuation timely by the measuring means 8 is held by a holding means 44. The inclination of the body 1 to be worked or electrode from the reference axis is computed by an arithmetic means 45 based on the measurement result held by the holding means 44. The correction computation which rotates the coordinate system by the reference axis is performed by a correction arithmetic means 43 based on the inclination computed by this inclination arithmetic means 45.