PURPOSE: To confirm a detected defect of a pattern due to dust, etc., on an exposure pattern directly and visually through two optical systems for exposure mask observation by scanning both optical systems simultaneously and performing comparing and inspecting operation.

CONSTITUTION: When a defect of an exposure mask image by a reduced projection type exposing device is inspected, X and Y stages 5 and 6 are operated manually to set an optical system 4 for left field observation at the inspection starting position 10 of an element pattern on the mask 1. Then, the optical system is put in operation to be set where the same adjacent element pattern with said inspection starting position 10 is observed. Both pictures of a left and a right visual field obtained from a TV camera 7 during the raster scanning of the X and Y stages 5 and 6 are compared with each other and checked, and only one-side image is judged as a defect; and stages are stopped there and an alarm is generated. At this time, the defect 9 is projected on a TV monitor 8 and the confirmation of operation is held in readiness. An operator discriminates them and inputs a next indication.