To enable an delivery of a gear pump to be switched arbitrarily by providing a rod member allowed to rotate in one body with the second drive gear shaft out of the first and the second drive gear shafts and to make movement in axial direction, and making both drive gear shafts to be connected to or separated from each other in response to the axial movement of the rod member.

When an electromagnetic solenoid 21 is set in its non-magnetized state, the tip of a rod member 16 is faced to an opening hole 17 and a drive gear 8 is rotated, te torque is transmitted to the rod member 16 via splines 18, 19b so as to rotate a drive gear shaft 9. Then, driven gears 2, 3 meshing with drive gears 6, 7 also make rotation to carry out ejection of fluid and then the total of ejection quantities of the first and the second pump mechanism is considered as the ejection quantity of a gear pump. Meanwhile, when the electromagnetic solenoid 21 is magnetized, the rod member 16 is moved and its tip is shifted from the opening hole 17, the drive gear shaft 9 is not rotated and only the ejection quantity of the first pump mechanism is defined to be the ejection quantity of the gear pump.