To reduce the cost of an inspection hole of a ceiling by enabling construction to be more easily performed than when a shaft is mounted on an inner frame.

The inspection hole of the ceiling is equipped with an outer frame 1 which is fitted into an opening of a ceiling board and fixed to the side of a building, and the inner frame 3 for opening/closing an internal space of the outer frame 1. A pair of opposed rising walls 4 of the outer frame 1 and a pair of opposed rising walls 5 of the inner frame 3 are connected by means of turning retainer members 6 which are attached to inner surfaces of the pair of opposed rising walls 4 of the outer frame 1, and turning members 8 which are provided integrally with corner connecting fittings 7 of the inner frame 3 in such a manner as to be protruded on outer surfaces of the pair of opposed rising walls 5 of the inner frame 3.