To provide: molds for in-mold foaming molding of a polyolefin-based resin, that are capable of suppressing the occurrence of burrs around a protrusion part of an insert member, said protrusion part protruding outward from a foaming molded article along a mold opening/closing direction in a molding step, and thus preventing a decrease in productivity and an increase in personnel costs caused by burr trimming; a method for manufacturing an in-mold foaming molded article; and an in-mold foaming molded article. Molds (11, 21) for integrally molding, with a foaming molded article comprising a polyolefin-based foamable resin, an insert member (4) that is provided with an embedded part to be embedded in the foaming molded article and a protrusion part (3a) protruding outward from the foaming molded article, said molds being provided with: a housing recessed part (32) in which the protrusion part (3a) can be housed; and an opening/closing means (40) provided with an opening/closing body (41), said opening/closing body (41) being capable of opening/closing an opening in the cavity (CA) side in interlock with the operations of inserting the protrusion part (3a) into the housing recessed part (32) and removing the same therefrom so that, when the protrusion part (3a) is inserted into the housing recessed part (32), the opening in the cavity (CA) side of the housing recessed part (32) is closed.