Abstract: A heat exchanger adapted to be mounted as required in the freezing chamber of a refrigerator so as to effect a rapid freezing. The heat exchanger comprises a heat exchanger body constituted by a pair of plates bonded by rolling to each other, the plate being made of a material having a high heat conductivity, the heat exchanger body having at least a horizontal portion and a riser portion protruding upright from one end of the horizontal portion integrally therewith, a plurality of first refrigerant passages formed between the two plates of the horizontal portion, a plurality of second refrigerant passages formed between the two plates in the riser portion, and a refrigerant charged so as to be circulated through the first and second refrigerant passages. The heat exchanger is mounted such that the riser portion opposes to the source of the chilled air, so that the refrigerant evaporated in the horizontal portion is liquefied in the riser portion and returned again to the horizontal portion.