Provided are an in-mold degassing structure, which acts by using no external control means, and a mold having that structure. The degassing structure comprises a sliding member (10) for receiving the pushing force of an elastic member from the bottom side, and a sliding member acceptor (20) for accepting the sliding member (10) slidably in the vertical direction. The sliding member (10) includes a vertical bottomed hole (12) communicating with a mold cavity and at least one side opening (13) communicating with the vertical bottom hole and opened to the side face. The sliding member acceptor (20) includes degassing ports (21) communicating in an initial state with the side opening (13) of the sliding member and closed when the sliding member is slid in a direction against the elastic member by the flow tip portion of the molten material. The degassing structure is mounted in the molten material flow passage or in the cavity near the trailing end of the molten material flow passage, thereby to degas the mold inside.