There is provided a pump system excellent in a maintenance ability and compatibility. The pump system comprises a pump (1) for transferring a liquid by alternately supplying air to air chambers (17a, 17b) to extend and contract a pair of bellows (13a, 13b) linked to a shaft (15). It also comprises a switching valve mechanism (2) for switching the air supplied to the pump (1). Switching mechanisms (40a, 40b) are employed to switch the pilot air for controlling the switching operation of the switching valve mechanism (2). The switching mechanisms are detachably attached to cases (16a, 16b) of the pump (1) from outside.