A mold for in-mold foam molding of polyolefin-based resin, the mold being configured to mold an insert member integrally with a foaming molded body, the insert member including an embedded part to be embedded into the foaming molded body formed from polyolefin-based resin pre-expanded beads and a protrusion part protruding from the foaming molded body toward the outside, wherein the mold for in-mold foam molding of polyolefin-based resin comprises: an accommodation concave part capable of accommodating the protrusion part; and an opening/closing means having an opening/closing part capable of opening and closing a cavity-side opening of the accommodation concave part in conjunction with insertion and extraction of the protrusion part into and from the accommodation concave part, so as to close the cavity-side opening in a state that the protrusion part is inserted into the accommodation concave part, wherein the opening/closing means includes an opening/closing part that is capable of swinging between an opening position at which the cavity-side opening is opened and a closing position at which the cavity-side opening is closed, and a biasing means for biasing constantly the opening/closing part to the closing position, and the opening/closing part comprises: an insertion-side opening operation part that abuts on the protrusion part and operates the opening/closing part to the opening position according to the insertion of the protrusion part into the accommodation concave part; and an extraction-side opening operation part that abuts on the protrusion part and operates the opening/closing part to the opening position according to the extraction of the protrusion part from the accommodation concave part. an accommodation concave part capable of accommodating the protrusion part; and an opening/closing means having an opening/closing part capable of opening and closing a cavity-side opening of the accommodation concave part in conjunction with insertion and extraction of the protrusion part into and from the accommodation concave part, so as to close the cavity-side opening in a state that the protrusion part is inserted into the accommodation concave part, wherein the opening/closing means includes an opening/closing part that is capable of swinging between an opening position at which the cavity-side opening is opened and a closing position at which the cavity-side opening is closed, and a biasing means for biasing constantly the opening/closing part to the closing position, and the opening/closing part comprises: an insertion-side opening operation part that abuts on the protrusion part and operates the opening/closing part to the opening position according to the insertion of the protrusion part into the accommodation concave part; and an extraction-side opening operation part that abuts on the protrusion part and operates the opening/closing part to the opening position according to the extraction of the protrusion part from the accommodation concave part. an insertion-side opening operation part that abuts on the protrusion part and operates the opening/closing part to the opening position according to the insertion of the protrusion part into the accommodation concave part; and an extraction-side opening operation part that abuts on the protrusion part and operates the opening/closing part to the opening position according to the extraction of the protrusion part from the accommodation concave part.