A resin molding die, comprising: a core mold comprising a protrusion formed on a surface thereof as an undercut, the protrusion being provided so as to form a through hole in a resin-molded product; and a cavity mold provided so as to be engageable with the core mold, wherein the cavity mold comprises: a main body comprising a first processing surface that is opposed to the surface of the core mold on which the protrusion is provided, under a state in which the cavity mold and the core mold are engaged with each other; and an insert provided to the main body so as to abut on the protrusion, the insert comprising a second processing surface as a surface thereof that abuts on the protrusion, characterized in that: the first processing surface comprises an embossed surface, the second processing surface comprises a mirror-finished surface, between the first and second processing surface is a continuous surface without gaps, and an area of the surface of the insert, which abuts on the protrusion, is larger than an area of a surface of the protrusion, which abuts on the insert, wherein the protrusion is provided so that a protruding direction thereof is orthogonal to the engaging direction in which the core mold and the cavity mold are engaged with each other, and wherein at least the second processing surface of the insert is formed of a material having a hardness larger than a hardness of the protrusion. a core mold comprising a protrusion formed on a surface thereof as an undercut, the protrusion being provided so as to form a through hole in a resin-molded product; and a cavity mold provided so as to be engageable with the core mold, wherein the cavity mold comprises: a main body comprising a first processing surface that is opposed to the surface of the core mold on which the protrusion is provided, under a state in which the cavity mold and the core mold are engaged with each other; and an insert provided to the main body so as to abut on the protrusion, the insert comprising a second processing surface as a surface thereof that abuts on the protrusion, a main body comprising a first processing surface that is opposed to the surface of the core mold on which the protrusion is provided, under a state in which the cavity mold and the core mold are engaged with each other; and an insert provided to the main body so as to abut on the protrusion, the insert comprising a second processing surface as a surface thereof that abuts on the protrusion, characterized in that: the first processing surface comprises an embossed surface, the second processing surface comprises a mirror-finished surface, between the first and second processing surface is a continuous surface without gaps, and an area of the surface of the insert, which abuts on the protrusion, is larger than an area of a surface of the protrusion, which abuts on the insert, wherein the protrusion is provided so that a protruding direction thereof is orthogonal to the engaging direction in which the core mold and the cavity mold are engaged with each other, and wherein at least the second processing surface of the insert is formed of a material having a hardness larger than a hardness of the protrusion. the first processing surface comprises an embossed surface, the second processing surface comprises a mirror-finished surface, between the first and second processing surface is a continuous surface without gaps, and an area of the surface of the insert, which abuts on the protrusion, is larger than an area of a surface of the protrusion, which abuts on the insert, wherein the protrusion is provided so that a protruding direction thereof is orthogonal to the engaging direction in which the core mold and the cavity mold are engaged with each other, and wherein at least the second processing surface of the insert is formed of a material having a hardness larger than a hardness of the protrusion.