PURPOSE: To enable transportation of plastic molten through a gear pump, by separating a portion of inner wall of a path contacting tightly with the gear face in the housing from other portion of housing and making the separated portion insertable from the end of path.

CONSTITUTION: A portion of the inner wall of path in a gear pump housing 1 is made insertable/removable and constituting a portion of the inner wall of path running in the proximity of the face of gears 2, 3 in the housing to exhibit annular appearance when viewed from the circumferential direction of the inner wall. A flange 41 is provided at the end of said section 4 to contact tightly with the inner face of the housing section 11 while removed freely from the housing 1 and the remaining section 11.