PURPOSE: To realize a contactless detection for either shape of a magnetic or nonmagnetic matter, by setting (n) units of vortex displacement detectors at divided areas in the width direction of a plate and making use of the output signals of these detectors.

CONSTITUTION: The (n) units of vortex displacement detectors 3 are set in a body in the width direction of a rolling stock. The enerigizing coil of the detector 3 is energized by the exciting frequency (10kHzW1MHz) of a sine wave oscillator 6. A compression air header 4 is set above the stock 2 to give a downward displacement to the stock 2. The gap between the stock 2 and each detector 3 is detected byaa detecting coil. The detecting signal is applied to an arithmetic device 100, and the shape detecting signals Δσ1WΔσn are obtained in response to the shape of the stock 2.