To reduce noise by hydraulic pressure fluctuation with a excellent follow-up in a small size, and to preclude the possibility of mixing of gas in oil in a hydraulic pump.

In this gear pump, a pair of driving gear 5 and driven gear 6 are arranged in a pump chamber 70, and a hydraulic fluid is sent out to a delivery chamber 72 from a suction chamber 71 by rotation of both gears 5, 6. This hydraulic pump is provided with a noise damper cylinder 20 having a capacity chamber 20a communicated with the delivery chamber 72, and is provided with a bottomed cylindrical elastomer member 32 having a peripheral wall part 33 and a bottom wall part 34 fixed in close contact to a peripheral wall surface 30 and a bottom wall surface 31 of the noise damper cylinder 20. The elastomer member 32 changes the volume to absorb the hydraulic pressure fluctuation.