To enhance an energy efficiency of a pump device for feeding a material fluid to a high pressure reaction container.

A production fluid produced by reacting the material fluid in the high pressure reaction container 14 is led to a back pressure pump chamber 18. The material fluid in a pressurization pump chamber 16 is pressurized by a pressure of the production fluid through a differential plunger 22 and is fed to the high pressure reaction container 14. The lacked part is fed to the high pressure reaction container 14 from a pressurization pump chamber 16 by further driving the pressurization plunger. The energy efficiency is enhanced by utilizing an energy of the pressure possessed by the discharged production fluid for pressurization and feeding of the material fluid.