An operation mechanism for an insertion device includes a moving section, an operation section configured to operate the moving section, a frame body fixed in the operation section, a long member movable along the frame body according to the operation of the operation section, a first tabular member provided between the frame body and the long member in the operation section, and a plurality of first projecting sections projecting from the first tabular member to the frame body side and disposed in a plurality of holes of the frame body.