To provide a gear pump wherein the discharge capacity is made variable according to a load.

In a casing, a driving gear and two driven gears biting each other to the driving gear are accommodated, and a main body 10 (double gear pump) of gear pump which actuates as the first pump 21 and the 2nd pump 24 in the 2 pipe lines are formed. The discharge port 23 and suction port of the second gear pump 24 are connected by an unloading passage 28, and in the unloading passage 29, an on-off solenoid valve 29 is provided. In the case of closing an on-off solenoid valve 29, the 1st and the 2nd pump 21 and 24 become the parallel running, and discharge capacity becomes large. In the case of opening the solenoid valve 29, the discharge capacity becomes small, since the 2nd pump 24 is unloaded.