A method of manufacturing a decoration piece comprising: forming a design piece made of thermoplastic synthetic resin with a design by high-frequency dielectric heating and by pressing with an engraving die and with an outer profile line by fusion cutting by means of high-frequency dielectric heating and by a fusion cutter; there being provided a lower layer, wherein said design piece is made of soft polyurethane, characterized in that there is also provided a dye migration preventing layer arranged between the design piece and the lower layer, in that said dye migration preventing layer has an outer profile which is the same as that of said design piece by virtue of that layer and the lower layer also being cut by the fusion cutter, and in that said dye migration preventing layer is a laminated film comprising a dye migration preventing film, a first intermediate layer, said first intermediate layer being arranged between said dye migration preventing film and said design piece, said first intermediate layer being thus fusion-bonded to said design piece, and a second intermediate layer, said second intermediate layer being arranged between said dye migration preventing film and said lower layer, said second intermediate layer being thus fusion-bonded to said lower layer, so that dye migration preventing layer is fusion-bonded to both said design piece and the lower layer by high-frequency dielectric heating, said dye migration preventing layer being capable of preventing any migrating of dye, in which either (i) said first intermediate layer is co-extruded with the dye migration preventing film and said second intermediate layer is co-extruded with the dye migration preventing film, or (ii) the said first intermediate layer is adhered to the dye migration preventing film by adhesive and the said second intermediate layer is adhered to the dye migration preventing film by adhesive. forming a design piece made of thermoplastic synthetic resin with a design by high-frequency dielectric heating and by pressing with an engraving die and with an outer profile line by fusion cutting by means of high-frequency dielectric heating and by a fusion cutter; there being provided a lower layer, wherein said design piece is made of soft polyurethane, characterized in that there is also provided a dye migration preventing layer arranged between the design piece and the lower layer, in that said dye migration preventing layer has an outer profile which is the same as that of said design piece by virtue of that layer and the lower layer also being cut by the fusion cutter, and in that said dye migration preventing layer is a laminated film comprising a dye migration preventing film, a first intermediate layer, said first intermediate layer being arranged between said dye migration preventing film and said design piece, said first intermediate layer being thus fusion-bonded to said design piece, and a second intermediate layer, said second intermediate layer being arranged between said dye migration preventing film and said lower layer, said second intermediate layer being thus fusion-bonded to said lower layer, so that dye migration preventing layer is fusion-bonded to both said design piece and the lower layer by high-frequency dielectric heating, said dye migration preventing layer being capable of preventing any migrating of dye, in which either (i) said first intermediate layer is co-extruded with the dye migration preventing film and said second intermediate layer is co-extruded with the dye migration preventing film, or (ii) the said first intermediate layer is adhered to the dye migration preventing film by adhesive and the said second intermediate layer is adhered to the dye migration preventing film by adhesive.