Method of inspecting die for forming honeycomb structure

A method of inspecting a die (1) having slits (2) of narrow widths and a number of rear apertures (3) communicating with the slits for forming honeycomb structures ascertaining roughness distributions on inner surfaces of the rear apertures of the die. The method includes irradiating diffused light beams onto an end face of the die on a side of the slits (2), detecting intensities of light beams arrived at an end face of the die on a side of the rear apertures (3) by irregular reflection at inner surfaces of the rear apertures by the use of photosensitive device such as sensitized paper (9) arranged at the end face of the die on the side of the rear apertures, and finally determining roughness distributions of the inner surfaces of the number of rear apertures from the bright and dark portions on the photosensitive device.