To solve a problem that in a gear pump, an engagement portion of a gear produces a confining zone confining an operation fluid, and sudden pressure fluctuation in the confining zone causes vibration and noise.

The confining zone 35 of the operation fluid is produced between engaging points A, B of a driving gear and a following gear. A notching portion 33 is provided on an edge portion 32 at an upstream side in a rotary direction X of a tooth root portion 31 of the gear 8. When the confining zone 35 is expanded to reduce pressure, the operation liquid flows in the confining zone 35 through a clearance groove 20 from a suction chamber 14. The operation fluid flows in the confining zone 35 smoothly by providing the notching portion 33. The vibration and noise are prevented by preventing generation of cavitation.