PURPOSE: To carry out a hydraulic pressure control quickly on discharge side and supply side by transmitting and receiving output signals of controlling devices on both discharge and supply sides through a radio equipment in case two or more pumps are operated in series connection.

CONSTITUTION: In case, for example, fire trucks are used in series, a supply pump 1 and a discharge pump 2 are driven by power taken out of running engines 3, 4 of two trucks, and water from a source 5 is supplied and discharged through a nozzle 6. A supply controlling device 9 inputs a signal from a feed water pressure detector 7, outputs a rotation control signal to the engine 3 and also outputs a supply control signal to a radio equipment 10 on supply side. A discharge controlling device 11 inputs a signal from a discharge water pressure detector 8, outputs a rotation control signal to the engine 4 and also outputs a discharge control signal to a radio equipment 12 on discharge side. According to this constitution, a hydraulic pressure control can be effected quickly on each discharge side and supply side.