To provide a window shade easily mounted on an automobile.

This window shade includes a guide rail device 45 constituting an interior panel. The interior panel includes a gap 48 for forming a groove slot 41 having a guide groove 16 at the same time. The guide groove 16 is undercut and is constituted of the groove slot 41 and a groove space 40 formed on back faces of the interior panel members 46 and 47. The rail 53 is fixed to the back faces of the two interior panel members 46 and 47, strides over the gap 48 and extends along the gap 48. The guide groove 16 is partially or completely formed within the rail 53.