A washing and drying machine comprising: - a cabinet forming the exterior of the washing and drying machine; - a tub mounted in the cabinet; - a drum rotatably provided inside the tub; - a drying duct, having a drying heater and a circulating fan, said drying duct supplying hot air into the drum to dry laundry; and - an air-cooling condensing unit that performs heat exchange between air introduced from the outside of the cabinet and at least a part of the tub to dry air used to dry the laundry in the drum, the air-cooling condensing unit comprising: an inlet port allowing outside air to be introduced into the cabinet, an outlet port allowing the outside air, which has passed the tub to be discharged out of the cabinet, and a condensing channel defined by the inside surface of the cabinet and the outer circumferential surface of the tub to allow the outside air introduced through the inlet port to flow between the outer circumferential surface of the tub and the inside surface of the cabinet and then guide the air such that the air is discharged out of the cabinet through the outlet port, characterized in that the cabinet includes a base pan, a cabinet body mounted on the base pan, a cabinet cover disposed in the front of the cabinet body, and a top plate mounted on the cabinet body and the cabinet cover; wherein the inlet port is formed at one side of the cabinet body, and the outlet port is formed at the other side of the cabinet body; wherein between the outer circumferential surface of the tub and the inside surface of the cabinet body is connected a third channel guide for directing the outside air such that the outside air makes partial contact with the outer circumferential surface of the tub; and wherein the condensing channel is defined by the outer circumferential surface of the tub, the inside surface of the cabinet body, and the third channel guide. - a cabinet forming the exterior of the washing and drying machine; - a tub mounted in the cabinet; - a drum rotatably provided inside the tub; - a drying duct, having a drying heater and a circulating fan, said drying duct supplying hot air into the drum to dry laundry; and - an air-cooling condensing unit that performs heat exchange between air introduced from the outside of the cabinet and at least a part of the tub to dry air used to dry the laundry in the drum, an inlet port allowing outside air to be introduced into the cabinet, an outlet port allowing the outside air, which has passed the tub to be discharged out of the cabinet, and a condensing channel defined by the inside surface of the cabinet and the outer circumferential surface of the tub to allow the outside air introduced through the inlet port to flow between the outer circumferential surface of the tub and the inside surface of the cabinet and then guide the air such that the air is discharged out of the cabinet through the outlet port, characterized in that the cabinet includes a base pan, a cabinet body mounted on the base pan, a cabinet cover disposed in the front of the cabinet body, and a top plate mounted on the cabinet body and the cabinet cover; wherein the inlet port is formed at one side of the cabinet body, and the outlet port is formed at the other side of the cabinet body; wherein between the outer circumferential surface of the tub and the inside surface of the cabinet body is connected a third channel guide for directing the outside air such that the outside air makes partial contact with the outer circumferential surface of the tub; and wherein the condensing channel is defined by the outer circumferential surface of the tub, the inside surface of the cabinet body, and the third channel guide.