To efficiently suction highly viscous grease at a low temperature in an expanded chamber pump for suctioning lubricant containing grease by reciprocating a pump tube dipped in a grease reservoir in respect to a plunger.

This pump is provided with a pump plunger 11 extended downward from a head 1 arranged on a supply source (vessel) 5 and a vertically reciprocatable lengthy pump tube 101 so as to surround the plunger 11. An eccentric part rotated by a motor 201 is housed in the head 1. The pump tube 101 is vertically reciprocated in respect to the plunger 11 by the rotation of the eccentric part. An induction check valve is arranged on the pump tube 101, adjacently to an open lower end on a lower end of the plunger. Suction and discharging of grease is performed by opening and closing an induction check valve, interlockingly with the reciprocation of the pump tube 101.