To discharge frying residues such as oil sediment and food pieces deposited on the bottom of an oil tank without being retained on the bottom, and to efficiently utilize the quantity of the frying oil and the calories for heating.

Foods 2 to be deep-fried are stored in a number of frying containers 4 of a food conveyer device 3, and the foods 2 are made to pass through the heated frying oil 6 inside one or at least two oil tanks 5 by moving the frying containers 4 along the trajectory of conveyance to deep-fry the foods 2 in the food deep-frying device 1. The inner bottom surface 7 of the oil tank 5 is inclined low toward an oil discharge port 8 so that the inner bottom surface 7 has enough gradient for the frying residues 9 in the frying oil 6 to slide from the upper part on the inner bottom surface 7 toward the lower oil discharge port 8. Further, an oil nozzle 10 is mounted downward on the inclined inner bottom surface 7.