An uninterruptible power supply device has a power supply circuit for supplying power from a power source to electronic equipment, a power interruption detection section for detecting interruption of the power supply from the power source, and a rechargeable battery charged by the power source. The uninterruptible power supply device further includes control means for controlling charging of the rechargeable battery in accordance with a charge state of the battery and also controlling the power supply from the rechargeable battery to the electronic equipment, and timer means for stopping the power supply to the control means after a lapse of a fixed time period from generation of a power interruption signal or shut-down signal, whereby wasteful consumption of electric energy stored in the rechargeable battery can be suppressed and also charge control for the rechargeable battery can be smoothly restarted at the recovery from power outage or at the start of the device.