A molding method for forming an impeller, includes a mold clamping process having a first mold for forming one side of blades, a second mold firmly clamped with the first mold, and a core arranged at the first mold relative to the blades, the mold clamping process clamping the first mold to the second mold in a state where the core is arranged between the first mold and the second mold, an injecting process injecting resin in a cavity obtained by the mold clamping process, and a mold removing process including the steps of releasing at least the first mold from the clamped state obtained by the mold clamping process to generate an opened portion in the first mold after the resin is hardened, rotating the core about a rotational axis toward the opened portion of the first mold, and separating the core from the resin-molded impeller.