A three-dimensional decorative piece that is made of a thermoplastic synthetic resin and can retain bulkiness and shape by a core and a method of producing the same. The three-dimensional decorative piece includes an upper layer molded body made of an upper layer material with a metal vapor-deposited layer and having a three-dimensional shape with a convex portion formed on its front surface side through a high-frequency dielectric heating, a core formed by curing a flowable synthetic resin filled in the convex portion of the upper layer molded body, and a substrate bonded a back surface side of the core by fusion.