In the present invention, a recuperator is used in a refrigerant cycle to make a heat exchange between a refrigerant generated in a condenser and a refrigerant before flowing into a compressor, thereby supercooling the refrigerant to minimize the quality of the refrigerant introduced into an evaporator, elevating temperatures at an inlet and an outlet of the compressor, and increasing condensed heat of the condenser. In the present invention, a recuperator is used to increase condensed heat of the condenser, leading to increasing the heat which circulation water circulating in a steam producing cycle receives from the condenser, whereby steam production efficiency can be improved.