PURPOSE: To easily exchange a packing gland device when the packing gland device is worn by enabling quick and easy extract of the packing gland device as a block from a pump chamber by a plunger, in the pump suitable for injecting concrete mixture.

CONSTITUTION: A stem 24 to be reciprocatively driven via a connection rod by revolution of a horizontal crank shaft is connected with a plunger 26 of a pump by a quick flange joint 27. The operation of this joint 27 is performed via an opening part 28 provided on an upper surface of a casing part 12. This opening part 28 can be closed by a hood. In front of a casing part 12, a block 31 having a pump chamber 33 is provided and is disposed adjacently to a packing device 34 for a packing gland 35 of the plunger 26 within each pump chamber 33. By opening the quick flange joint 27, the packing device 34 and the plunger 26 corresponding to the device 34 can be taken out through the opening part 28.