PURPOSE: To provide a gear pump which is favorable to a manufacturing cost and a delivery even when specifications are differed with viscosity and an amount of working high viscosity liquid.

CONSTITUTION: Formation of a pump is such that a drive shaft 4 and a driven shaft 5 are supported by bearing parts 7, 8, 9, and 10 arranged in a pump chamber and liquid is conveyed through engagement of a pair of gears 4G and 5G fixed to the drive shaft 4 and the driven shaft 5, respectively, and liquid on the high pressure side to be conveyed is guided through a lubrication passage M2, formed in the inner peripheral surfaces of the bearing parts 7, 8, 9, and 10, from the gear side to the outside to lubricate the bearing parts 7, 8, 9, and 10. The end parts on the outside of the bearing parts 7, 8, 9, and 10 are constituted as removable replacing members 11 and 12 and different lubrication passages are formed in the bearing parts 7, 8, 9, and 10 of the replacing members 11 and 12.