To obtain a fried product of quality while foods is prevented from being conglomerated and half-fried due to adhesion of foods when the foods contained in a food case are deep-fried under vacuum.

A food case 2 has a porous bottom plate 2a, a non-porous sidewall 2b and a non-porous top cover 2c, and steam exhaust slits 4 are partly provided in an upper area of the sidewall 2b above the middle line. Foods to be cooked are put in the food case 2 and immersed in hot oil in a vacuum frying vessel for a specified time period to perform frying treatment. Thereby, a steam layer is formed in the upper part inside the food case 2 when the steam generated from the foods flows out through the exhaust slits 4, that prevents the foods that float up from being pushed against the cover 2c. The steam streams make the hot oil flow and the foods is adequately agitated by the steam and hot oil streams, so that the foods are prevented from being conglomerated and half-fried due to adhesion of the foods.