To eliminate a change of output pressure due to that a pressure booster is formed into compactness and a set up attitude is changed, by forming a switch valve as a pilot type.

A switch valve 28 provided in a center body 22 of a pressure booster 21 is formed as a switch valve of pilot type having a main valve 46 supplying driving compressed air to and discharging it from drive chambers 38A, 38B by supplying pilot air to and discharging it from a pilot chamber 49 and pilot valves 47A, 47B operated by pressing of pistons 34a, 34b to supply pilot air to and discharge it from the pilot chamber, to separately set up the main valve 46 in a direction orthogonal to a moving direction of the piston and the pilot valve in a direction orthogonal to a moving direction of the piston.