To provide a gear pump which materializes reduction of liquid leakage between a pump chamber and an inside space.

In a pump part 11 of a two stage gear pump 1, the inside space is formed in a position around a cylindrical surface 29a of a driven shaft 29 and adjacent to gears 32, 33. The inside space 52 communicates with a communicating passage 43 for communication between a discharging side of a first-stage gear train 36 and a inlet side of a second-stage gear train 37 through the medium of a pressure introduction passage 67. The inside space 52 is made to be an intermediate pressure atmosphere between inlet pressure and discharge pressure of the pump part 11 by introducing the pressure from the communicating passage 43 through the pressure introduction passage 67.