Disclosed is a deterioration determination device for a liquid pumping apparatus including: a casing that forms a reservoir space for storing liquid flowed thereto; a feed valve that introduces working gas into the reservoir space; an exhaust valve that releases the working gas from the reservoir space; and a valve operating mechanism having a float arranged in the reservoir space, and performing a pumping stroke in which the liquid is pumped from the reservoir space under a pressure of the working gas by opening the feed valve and closing the exhaust valve when the float moves up to a predetermined high level, and an inflow stroke in which the liquid flows into the reservoir space and the working gas is released from the reservoir space by closing the feed valve and opening the exhaust valve when the float moves down to a predetermined low level. The deterioration determination device includes a first pressure sensor arranged to communicate with a lower portion of the reservoir space to detect a pressure of a liquid layer in the reservoir space, and a deterioration determination unit that determines a degree of deterioration of the valve operating mechanism based on a change in the pressure detected by the first pressure sensor.