PURPOSE: To inject normal fire extinguishing foaming liquid with a specified foam mix ratio by setting a foam concentrate mixer to a pipe system of the discharge side of a discharge pump when a water source of a minus water suction head is sucked with the discharge pump through a valve operation and setting said mixer to a pipe system of the water sucking side when the water source of the plus water suction head is absorbed.

CONSTITUTION: When a water source has a normal water level E of a water head, valves 1, 2, 3 are opened and valves 4, 5, 6 are closed to drive pumps P, Q. Water is discharged from a nozzle through an intake 7, a discharge pump P and a mixer M. Foam concentrate is then mixed into the mixer M by a pump Q with a normal mix ratio. When the water source has fire hydrant S of plus water head, valves 4, 5, 6 are opened and valves 1, 2, 3 are closed to run the pumps P, Q. Water is discharged from the nozzle through the fire hydrant S, mixer M and discharge pump P. While the mixer M is at the water absorption side of the discharge pump P, pressurized water at the water absorption side of pump, pressurized water of plus water head flows in so that foam concentrate is poured in by the foam concentration pump Q. The same requirement as the foam concentration is mixed in the mixer at the discharge side of pump is obtained so that the mix ratio of water and foam concentrate becomes normal.