To provide a cover for underground structure which can prevent the occurrence of the level difference between a cover body and a receiving frame when the cover body is closed and which can surely house the cover body in the receiving frame in a horizontal state.

A cover 1 for underground structure comprises a receiving frame 3, a hinge seat 8 projecting to the inside of the receiving frame 3 and having a mounting part 8b at the tip and a hinge insertion hole 8a at the center, a hinge 4 which has a shank part 9 inserted into the hinge insertion hole 8a of the hinge seat 8, and a slip-off stop piece 5 at the bottom edge and a head part 6 at the top edge, and a cover body 2 installed to be opened/closed with respect to the receiving frame 3 through the hinge 4 installed to be swingable to the lower side. In the cover 1 for underground structure, the shank part 9 of the hinge 4 is provided with a recess 11 having a curved surface curving in a longitudinal section, and in the mounting part 8b of the hinge seat 8 at least a part of the top face on the side facing the hinge insertion hole 8a follows the curved surface.