Plastic window panel

A plastic sun roof panel has a central portion formed in a maximum and uniform thickness. Further, a mounting portion having a minimum and uniform thickness is formed annularly along a peripheral edge portion. Between the central portion and the peripheral edge portion, there is annularly formed a tapered portion whose thickness is gradually reduced from the central portion toward the mounting portion. A reinforcing member is arranged so as to extend along the peripheral edge portion of the sun roof panel, and is fastened to the plastic sun roof panel by means of an adhesive. A flange of the reinforcing member is fitted into a weather strip. In the peripheral edge portion, the tapered portion is situated on the inner side of the mounting portion to which the adhesive is applied.