The present process includes a mold for producing a thermoplastic resin molded article, comprising paired sliding female and male mold members, which mutually slide at the time of mold closing. A product-forming portion and a non-product-forming portion are provided in the cavity of the mold, the mold further including a resin-supplying opening. A gate portion located at a boundary between the product-forming portion and non-product-forming portion interconnects the two portions. At closing of the mold, the width of the gate at the product-forming side is less than the thickness of the formed product, and stepwise or continuously widens toward the non-product-forming side. Using this mold, a thermoplastic resin molded article, with or without a laminated skin material, can be molded in good efficiency and low cost, further having a non-product-forming portion, which can be readily trimmed from the product-forming portion.