PURPOSE: To provide a redundant uninterruptible power-supply system at low cost with a small installation area in construction, by reducing the capacity of power storing unit without lowering reliability.

CONSTITUTION: In this system for feeding power to a load wiring, a plurality of uninterruptible power supply units 1, 2,...n+1, with one more unit than the necessary units for supplying power uniformly to a load 15, are connected in parallel. Each uninterruptible power supply unit has an AC/DC converting means 10 and a DC/AC converting means 12 connected with the converting means 10 on the output side. A switching means 21 is put on the output side of the AC/DC converting means 10 for selecting an individual power storage unit wiring 22 or a common transfer wiring 23 in connection. Each power storage unit wiring 22 is connected to the transfer wiring 23 through a forward direction joining means 24. A battery unit 11 is connected to all the power storage unit wirings 22 except for one power storage unit wiring 22.