PURPOSE: To obtain a high decorative effect by forming a paint film with less elongation than that of a thermoplastic resin plate on the surface of the translucent thermoplastic resin plate, and molding it into a recessed shape under heat.

CONSTITUTION: An illumination apparatus has an illumination cover 2 formed with a plate material into a semi-spherical shape, and an illumination lamp 3 is stored at the center section of the inside. The illumination cover 2 is constituted of a substrate made of thermoplastic resin and a paint film 5 coated or printed on one face of it. Tortoise shell-shaped cracks 6 are generated on the paint film 5 when the illumination cover 2 is heat-molded, and the cracks 6 have a width W. Recessed grooves 6a are formed at portions of the substrate 4 corresponding to the cracks 6, and recessed grooves 10 are formed at portions of the inside face 7 of the illumination cover 2 corresponding to the cracks 6. A decorative effect in the room is obtained even when the illumination lamp 3 is not lighted, and the light is refracted and scattered on irregular faces when it is lighted, and a lighting decorative effect can be obtained.