PURPOSE: To perform operation of an on-off valve located in a bypass flow passage according to the rapid fluctuation of a delivery pressure without the occurrence of hunting during normal operation.

CONSTITUTION: A fuel compressor 1 for a gas turbine comprises a bypass flow passage 6 communicated to a suction flow passage 5 through an on-off valve 4 located in the delivery passage 3 of a compressor body 2 and a pressure control device 7 located in the delivery passage 3 in a manner to be capable of detecting a pressure and outputting a signal to the on-off valve 4, by means of which the opening of the on-off valve 4 is increased when a detected pressure exceeds a given range and the opening of the on-off valve 4 is decreased when it is below a given range. The pressure control device 7 is formed so that a control gain when a detected output is outside a predetermined delivery pressure range is increased to a value higher than a control gain when the detected pressure is within the range.