A pump unit 10 includes: a housing 13 provided with an inlet 11 and an outlet 12 for a fluid； and a pump group composed of micro pumps 15 arranged in the housing 13, for allowing a fluid entering through the inlet 11 to exit from the outlet 12. The pump group includes: the micro pump 15 positioned in the most upstream (m1)； the micro pump 15 positioned in the most downstream (m4)； and the micro pumps 15 positioned in the middle (m2 to m3). The housing 13 includes: an inlet direct-connecting flow passage 41 directly connecting a suction port 31A of the micro pump 15 positioned in the most upstream with the inlet 11； an outlet direct-connecting flow passage 42 directly connecting a discharge port 31B of the micro pump 15 positioned in the most downstream with the outlet 12； and a flow passage forming mechanism switchable between a state in which the micro pumps 15 are connected in series and a state in which the micro pumps 15 are connected in parallel.
