Abstract: A method for operating a plural number of batch type reduced-pressure fryer units, the method including: connecting the fryer units, through a switch means, with vacuum pump lines including an initial vacuum pump line serving to reduce the frying bath pressure of a selected one of the fryer units in the stage of an initial frying treatment and a finish vacuum pump line serving to maintaining the frying baths of a plural number of the frying units simultaneously in reduced pressure condition in the stage of a finish frying treatment; while holding the respective vacuum pump lines in operation, switching the vacuum pump lines to connect the initial vacuum pump line with a selected fryer unit to reduce the pressure of the frying bath thereof for the initial frying treatment; switching the vacuum pump line to connect the selected fryer unit with the finish vacuum pump line for the finish frying treatment upon completion of the initial frying treatment; switching the vacuum pump lines to disconnect the selected fr