Abstract: A production method for a resin molding (1) inserted a 1st plate (10) having many through holes (10a) and a 2nd plate (11) having many through holes (11a), which are arranged in parallel and facing each other during a manufacturing process, comprising a 1st plate process and a 2nd plate process. The 1st plate process in which, the 1st plate (10) moves to the 2nd plate (11) side from a 1st plate start position (U0) and returns a 1st plate end position (P3) near the 1st plate start position (U0) in a cavity filled with a molten resin (4) kept to a high pressure. The 2nd plate process in which, the 2nd plate (11) moves to the 1st plate (10) side from a 2nd plate start position (V0) and returns a 2nd plate end position (P4) near the 2nd plate start position in the cavity. This makes it possible to spread the molten resin (4) to even a shielded area with a reciprocal plate motion.