PURPOSE: To obtain a foam molding die free from jamming up in steam holes and easy to preparation by a method wherein a core vent as the steam hole of the foam molding die is formed by resin of high heat resistance, fitted to the die before heat treated and stuck to the die.

CONSTITUTION: In a foam molding die, the part 11 shows an inner die on the side of a cavity die 10, the part 21 shows the inner die on the side of the core 20, A shows the mold space built between two inner dies 11, 21, the part 30 shows the core vent as a steam hole part made on the die space wall of each inner die. Said core vent 30 is molded by resin such as polyphenylene sulfide etc. that does not change at foam molding temperature, is of high heat resistance temperature or hardens at the specified temperature of higher, inserted into the die space wall, then heat treated, hardened and stuck to the wall. Said core vent 30 is prevented effictively from thermal change, and is not removed so easily by temperature rise due to foaming.