PROBLEM TO BE SOLVED: To establish a substantial small-sized formation of a pump unit 10 while improving fluid transportation capability.SOLUTION: A pump unit 10 includes a casing 13 provided with a fluid inlet 11 and a fluid outlet 12, and a group of pumps composed of micropumps 15 arranged inside the casing 13 so as to discharge fluid entered at the inlet 11 to the outlet 12. The group of pumps have a micropump 15 positioned at the upper-most stream side [m1], a micropump 15 positioned at the most-downstream side [m4] and micropumps 15 positioned at intermediate sides [m2 to m3]. The casing 13 includes: an inlet direct connection flow passage 41 directly connecting a suction inlet 31A and the inlet 11 of the micropump 15 positioned at the upper-most stream side an outlet direct connected flow passage 42 for directly connecting a discharging port 31B and the outlet 12 of the micropump 15 positioned at the lower-most stream side and a flow passage forming mechanism freely changeable between a state in which micropumps 15 are connected in series and a state in which the micropumps 15 are connected side-by-side.SELECTED DRAWING: Figure 9
