Provided is a technology that sufficiently suppresses dimensional change in the usage environment even without applying heat treatment in advance to a resin-molded article constituted of a crystalline thermoplastic resin. A resin composition constituted of a crystalline thermoplastic resin is injection-molded using a mold on the inner surface of which a heat-insulating layer is formed. It is preferable, in the present invention, to use a mold on which a heat-insulating layer is formed, the layer being constituted of porous zirconia formed by spraying method and having a thermal conductivity of 2 W/(m·K) or less and a thickness of no less than 200 μm. The injection-molded article obtained by the manufacturing method of the present invention has a dimensional change rate of 0.2% or less when left for 2 hours in an environment of a mold temperature+20° C. where the mold temperature is that at the time of injection molding and is Tg+30° C. or more and Tg+80° C. or less, in which Tg is a glass transition temperature of the crystalline thermoplastic resin.