PURPOSE: To prevent a pump from wearing and corroding due to suspension material and lengthen its life by jetting lubrication oil from a lower circumference of a pump plunger formed under a main plunger along a circumferential inner face of a pump cylinder as the main plunger comes down.

CONSTITUTION: The constitution shall be arranged in such that lublication oil (a) supplied from a lubrication oil supply apparatus L through a uniform gap 34 formed circumferentially on a lower portion of a pump plunger Pa2 formed under a main plunger Pa can be ejected onto an circumferential inner face of a pump cylinder Pa2 during descending of the main plunger Pa of a main pump body P. Consequently, any sand, silt, and sludge, etc. contained in heavy oil adhering onto a circumferential inner face of the pump cylinder Pa2 are effectively cleaned out in order to prevent a circumferential outer face of the pump plunger Pa2 and a circumferential inner face of a pump cylinder Pb2 from wearing and corroding due to suspension such as sand and the like. Thus, the life of the pump body P can be extended.