PURPOSE: To perform measurement simply and quickly and to improve accuracy, by rotating an object to be measured by a rotary table, and obtaining a plurality of measured data based on the difference in spans to noncontact sensors.

CONSTITUTION: The object to be measured is set on the rotary table 17, and the noncontact sensors 31a and 31b are positioned in the range wherein inherent measurement can be performed. Then, the rotary table 17 repeats the rotation and stop automatically. When it is stopped, a high frequency power source is operated based on a control signal, and the measurement of the object to be measured is performed by the noncontact sensors 31a and 31b.