PURPOSE: A part such as a plastic plate for a thin-shaped watch, having high stength and reliability, not requiring post process, obtained by injection molding a thermoplastic resin blended with glass fibers in a specific shape.

CONSTITUTION: A thermoplastic resin blended with glass fibers having diameters of 5W7μm and length of 100W150μm is injection molded, to give a plastic part having a thickness at the gate part by the injection molding of ≤1mm. The height (the thickness of the resin part 12a+the length of the glass fibers 12b standing on it) of the gate cutting trace 12 remaining at the gate part A of the plastic plate 10 prepared by injection molding is made smaller than the depth of the dent part 11 of the gate, the cutting trace 12 is lowered than the height of the dent part 11, so that it has no influence on the face 10 to which parts are attached.