To provide a volume type liquid supply mechanism capable of discharging liquid without interruption.

This supply mechanism is constituted in such a way that a rotatable plunger 15 is fitted into a cylinder 11 whose both ends are blocked by a lid body 21 and which is slidable in the axial direction to form pump chambers 24a, 24b surrounded by the cylinder 11 and the lid body 21 on both sides outside of the plunger 15. The cylinder 11 is provided with a pair of suction holes 11a, 11b at positions facing the plunger 15 at all times in a scope of slide and is provided with discharge holes 11c, 11d by corresponding to angle positions obtained by turning from angle positions of these suction holes by 180 degrees, respectively.