A method for manufacturing a foam molded body, comprising a step of forming a foam parison by melting and kneading a raw material resin and a foaming gas in a cylinder of an extruder to obtain a melt-kneaded resin, storing the melt-kneaded resin in a cylinder of an accumulator, and after a predetermined amount of the melt-kneaded resin is stored in the cylinder of the accumulator, moving a piston of the accumulator to extrude the melt-kneaded resin from a die slit provided in a head, and a step of molding the foam parison using split molds to obtain the foam molded body, characterized in that the molding is a blow molding in which the foam parison is molded by blowing air into cavity of the split molds, and the foaming gas is a gas obtained by removing oxygen from air with an absorbent, wherein the foaming gas is supplied from a nitrogen gas generation unit which removes oxygen from air by using the adsorbent; the nitrogen gas generation unit comprises: a first compressor for compressing air, a tank for storing the compressed air produced by the first compressor, a nitrogen gas generator adapted to remove oxygen from the compressed air stored in the tank by using the adsorbent, a first buffer tank for storing nitrogen gas whose purity is increased by the nitrogen gas generator, a second compressor for increasing the pressure of the gas stored in the first buffer tank, and a second buffer tank for storing the gas whose pressure is increased by the second compressor; and the foaming gas is supplied to the cylinder of the extruder from the second buffer tank. a step of forming a foam parison by melting and kneading a raw material resin and a foaming gas in a cylinder of an extruder to obtain a melt-kneaded resin, storing the melt-kneaded resin in a cylinder of an accumulator, and after a predetermined amount of the melt-kneaded resin is stored in the cylinder of the accumulator, moving a piston of the accumulator to extrude the melt-kneaded resin from a die slit provided in a head, and a step of molding the foam parison using split molds to obtain the foam molded body, characterized in that the molding is a blow molding in which the foam parison is molded by blowing air into cavity of the split molds, and the foaming gas is a gas obtained by removing oxygen from air with an absorbent, wherein the foaming gas is supplied from a nitrogen gas generation unit which removes oxygen from air by using the adsorbent; the nitrogen gas generation unit comprises: a first compressor for compressing air, a tank for storing the compressed air produced by the first compressor, a nitrogen gas generator adapted to remove oxygen from the compressed air stored in the tank by using the adsorbent, a first buffer tank for storing nitrogen gas whose purity is increased by the nitrogen gas generator, a second compressor for increasing the pressure of the gas stored in the first buffer tank, and a second buffer tank for storing the gas whose pressure is increased by the second compressor; and a first compressor for compressing air, a tank for storing the compressed air produced by the first compressor, a nitrogen gas generator adapted to remove oxygen from the compressed air stored in the tank by using the adsorbent, a first buffer tank for storing nitrogen gas whose purity is increased by the nitrogen gas generator, a second compressor for increasing the pressure of the gas stored in the first buffer tank, and a second buffer tank for storing the gas whose pressure is increased by the second compressor; and the foaming gas is supplied to the cylinder of the extruder from the second buffer tank.