Abstract: A fryer is provided which, during a standby for cooking, can keep the temperature of a cooking oil slightly lower than a cooking temperature and, during cooking, can quickly raise the oil temperature to the cooking temperature. The fryer also has capabilities of easily performing a heat exchange operation on the cooking oil, preventing degradation of the cooking oil, securing a good kitchen environment and enhancing a work efficiency. The fryer comprises a fryer tank having oil and water for cleaning the oil stored in two layers one upon the other; and a heater installed in the oil layer; wherein the water in the water layer is drawn out from a water suction opening at a bottom of fryer tank, cleaned by a filtering water tank and then delivered into the fryer tank almost horizontally in an off-centered direction from a water supply opening formed in a lower, side wall of the fryer tank, thus rotating the water in the fryer tank in a swirl.