To fix a designated parts on a plate-shaped body without play, not to be loosened up.

An edge part of a mounting hole of an interior panel 16 as a plate shaped body is fixed by pinching with a housing 12 retaining a lighting bulb and a part above a flange of a lens 14. A projection 28 is provided on an inner peripheral surface 26 of the housing 12. A vertical groove 38 extending in a shaft direction and a horizontal groove 40 extending in a circumference direction are provided on an outer peripheral surface 34. When the lens inserted in the housing , the projection is guided along the vertical groove and when the lens is rotated, the projection moves along the horizontal groove. The projection rides over a slope 46 of a bottom surface of the horizontal groove to push out the housing. When the lens is rotated more, the lens falls into a hole 42. The housing and the lens are assembled by that. Since stress applied on the projection is small, deformation of bulb due to heat is prevented, and play and looseness are prevented.