Abstract: An injection molding method for a plate-shaped resin substrate, wherein a through-hole whose diameter gradually becomes smaller from one surface to the other surface is provided thereon and fine flow path that connects to the through-hole is provided on the other surface. A cavity is formed by joining one molding die forming one surface with the other molding die forming the other surface. A part of the one molding die that forms the through-hole includes a taper pin that protrudes from the one molding die toward the other molding die. The substrate is formed by filling the cavity with resin material, and the substrate is released from the other molding die by separating the one molding die from the other molding die. By pushing the inner wall of the through-hole with the taper pin projected further toward the other molding die, the substrate is released from the one molding die.