A cover includes a cover body, a grommet, and a projection. The cover body includes a socket disposed on one of the front and rear opposite surfaces. The grommet is deformable, is held in the socket, and includes a fitting hole. The projection projects from an installation member to which the cover is installed, and is fitted into the fitting hole of the grommet, whereby holding the cover body detachably to the installation member. The grommet further includes convexities disposed on the outer peripheral surface at least, protruding in radial directions, and contacting with the inner peripheral surface of the socket at least. By the elastically deforming convexities, not only the cover is improved in terms of the attachment and detachment operability but also is enhanced in terms of the stability when being installed to the installation member.
