To provide a compressor unit capable of improving maintenance performance of a buffer tank and an oil separator disposed on a bottom plate without increasing an installation area.

In this compressor unit 10 comprising a compressor 21 compressing a helium gas, an outdoor heat exchanger 22, the oil separator 23 and the buffer tank 24 in a housing 10A, and constituted to supply the compressed helium gas to a refrigerating machine 11 realizing ultralow temperature, the oil separator 23 and the buffer tank 24 are disposed on the bottom plate 41 of the housing 10A approximately in parallel with each other and obliquely to the longitudinal direction of the bottom plate 41, and mounting members 23B, 24B respectively for mounting the oil separator 23 and the buffer tank 24 to the bottom plate 41, are disposed on the oil separator 23 and the buffer tank 24 in a state that they are not overlapped to each other when seen head-on.