PURPOSE: To facilitate disassembly and cleaning of a gear pump, by a method wherein an opening part, which is insertable in a condition to engage gears with each other, is provided in a housing, and a clamp member, which prevents dislocation of a bearing case from the housing, is installed.

CONSTITUTION: An opening part 25, which is insertable in the direction of an axis in a condition to engage a pair of gears 13 and 14 with each other, is formed in a housing 7, and a bearing case 20 is closely mated with the opening part. Projecting parts 26 and 27, which are brought into contact with each other, are radially located in a projecting manner to the periphery of the opening part and the bearing case, and the projecting part has two sides forming a tapered surface 29 through the medium of a contact surface 28 extending in an axial direction. A clamp member 30, which is engaged outwardly with the tapered surface 29 for taper engagement and prevents dislocation in an axial direction a bearing case from a housing, is mounted so that is can freely engage with and disengage from the projection parts 26 and 27.