PURPOSE: To provide a gear pump that can surely discharge highly viscous fluid from a vacuum towards a high pressure with a small delivery pressure.

CONSTITUTION: An area of inlet 4, an area of outlet 6, and a pair of gear wheels 2 are provided in a housing 3, highly viscous fluid is coming from a vacuum to a high pressure area. The inlet 4 has a hopper shaped enlargement 10 that extends at least as far as the plane 11 at the same level as the gear wheel axes 12. The hopper shaped enlargement 10 is parallel to the plane 11 and at right angle to the gear wheel axes 12. The length R of the hopper shaped enlargement 10 is larger than the length D of the pair of the gear wheels 2. The hopper shaped enlargement 10 has a width C greater than tooth width T in the direction of the gear wheel axes 12 at the same height as the gear wheel 12.