There are provided (1) a method of manufacturing a three-dimensional decoration piece having a flat rear surface, (2) a method of manufacturing the decoration piece by easily cutting the same by means of a fusion cutter, (3) a method of manufacturing the decoration piece having a bonding or sticking feature on the rear surface and (4) a method of manufacturing a three-dimensional decoration piece without limiting the characteristics of the base member thereof.The three-dimensional decoration piece is manufactured by using an indented mold and high frequency dielectric heating. An indented mold having a second fusion cutter and arranged along an outer periphery of the fusion cutter is used. Firstly, a three-dimensional molded body of upper and intermediate layers having a recessed section on a lower surface thereof is molded by means of an indented mold and a protruding mold, and subsequently a lower layer material is molten by high frequency dielectric heating and made to flow into the recessed section. Firstly, a three-dimensional molded body of upper and intermediate layers is molded, and subsequently the three-dimensional molded body is welded to a base member by means of high frequency dielectric heating.