An injection molding machine includes a gas feeding mechanism configured to feed gas to a cavity formed between a first mold plate and a second mold plate in a clamped state; an injection apparatus configured to inject a foamable resin into the cavity having an inside pressure thereof increased to be higher than an atmospheric pressure by the gas feeding mechanism; and a gas releasing mechanism configured to release the gas inside the cavity to an atmosphere through a gap formed between an inner wall surface of a through hole formed through one of the first mold plate and the second mold plate and an outer circumferential surface of a mold member inserted into the through hole, during or after the injection of the foamable resin by the injection apparatus.