The present invention is intended to provide a mold for in-mold foam molding of polyolefin-based resin that prevents the occurrence of burrs around protrusion parts of insert members protruding from a foaming molded body toward the outside in a mold opening/closing direction at the time of molding to control productivity reduction and labor cost rising caused by burr trimming, a method for manufacturing an in-mold foaming molded article, and the in-mold foaming molded article. A mold 11 and 21 is configured to mold an insert member 4 including an embedded part to be embedded into a foaming molded body formed from a polyolefin-based resin and a protrusion part 3a protruding from the foaming molded body toward the outside integrally with the foaming molded body. The mold 11 and 21 is provided with an accommodation concave part 32 capable of accommodating the protrusion part 3a and an opening/closing means 40 having an opening/closing part 41 capable of opening and closing a cavity CA-side opening of the accommodation concave part 32 in conjunction with insertion and extraction of the protrusion part 3a into and from the accommodation concave part 32 such that, while the protrusion part 3a is inserted into the accommodation concave part 32, the cavity CA-side opening is closed.