PURPOSE: To measure the glossiness without contact at a high speed under the externally disturbed light, by irradiating light on a specimen piece through slits forming radial small gaps and receiving interfered light generated on the specimen piece caused by said irradiation in a light receiving device.

CONSTITUTION: The gloss detector judges the gloss by utilizing the interference light generated on the concave and convex surface of the specimen piece 1 with the depth of 1μm and less. When the lines of the light are radially arranged, and linear lines of the light are converged in the vicinity of the center. Therefore the area wherein the lines cannot be distinguished is formed. Thus as an image as a whole, it looks as if a circle has appeared at the center due to the interference light. The diameter of the circle for poor gloss is large, and that for the good gloss is small. Therefore, by receiving said interference light 1 by a TV camera 8 as a light receiving device, the glossiness can be measured at a high speed under the externally disturbed light.