To prevent a large decrease in damping force of a damper for damping rotation with viscous liquid filled between opposed faces, with simple structure.

A damper has a first and a second members 10, 20 having annular grooves 13, 22 and annular protruding parts 12, 23 accommodated in the grooves 13, 22, and rotatably combined by accommodating the protruding parts 12, 23 in the grooves 13, 22, and viscous liquid 30 filled between the opposed faces M of the first and second members 20. Spaces (y) between groove bottom faces 40b of the grooves 13, 22 and the tip faces 41b of the protruding parts 12, 23 out of the faces of the grooves 13, 22 and protruding parts 12, 23 forming at least part of the opposed faces M are larger than spaces between groove side faces 40a of the grooves 13, 22 and side faces 41b of the protruding parts 12, 23.