PURPOSE: To realize high speed, highly accurate, noncontact measurement of thickness without requiring setting of a reference surface by irradiating an object to be inspected with a laser beam on the both opposite faces thereof and detecting displacement of surface based on the reflected light thereby determining the thickness.

CONSTITUTION: Laser light emitted from a semiconductor laser 1 passes through a projection lens 2 to produce a laser beam 3, which impinges obliquely on the surface of a frame 7. Regularly reflected laser light 8 is passed through a condenser lens 9 and focused on the detecting surface of a position detecting element 10, and surface displacement of the frame 7 is then determined according to the triangulation principle based on the focal point on the detecting surface. Similarly, laser light emitted from a semiconductor laser 11 is focused on the detecting surface of a detecting element 16 and the focal position is employed in the measurement of surface displacement of a pellet 5. When the outlets of the elements 10, 16 are set depending on the thickness of an object 4 to be inspected, overall thickness of the object 4 can be determined. Thickness of each of the frame 7 and the pellet 5 is then measured at a stripped part thereof and subtracted from the overall thickness thus determining the thickness of paste 6. This apparatus realizes high speed, highly accurate, noncontact measurement.