Patent attributes
An inner peripheral portion of a receiving frame and an outer peripheral portion of a lid body each include first and second surface parts. In the closed-lid state, the first surface part of the lid body is supported by the first surface part of the frame, each of which include a gentle gradient. The second surface parts of the lid body and the receiving frame are pressed against each other by a force caused by elastic deformation of at least one of the outer peripheral portion of the lid body and the inner peripheral portion of the receiving frame. The second surface part of the receiving frame includes a steeper gradient than the first surface part of the receiving frame by reducing its diameter toward a downward direction of the receiving frame.
