PURPOSE: To facilitate detection of a translucent organic foreign substance and improve the ability of foreign substance detection by a method wherein exciting light is applied to a mask to be inspected with the optimum angle and both reflected light and fluorescent light emitted from the foreign substance are detected.

CONSTITUTION: When no foreign substance exists on a mask 8 to be inspected, exciting light 91 from an exciting light oscillator 9 is reflected normally by the surface of the mask and does not enter an exciting light detector 10 and a fluorescent light detector 11. When a foreign substance 81 exists, if the foreign substance 81 is an inorganic substance which does not emit fluorescent light, the exciting light 91 applied to the foreign substance 81 is scattered and detected by the exciting light detector 10 so that the existence of the foreign substance 81 can be recognized. If the foreign substance 82 is a translucent organic substance, the exciting light 91 itself is transmitted through the foreign substance 82 but fluorescent light 92 which is excited by the light 91 is emitted and detected by the fluorescent light detector 11 so that the existence of the foreign substance 82 can be recognized.