An emergency electric power supply unit (9) for backing up the main electric power supply system (1, 10) at the time of the malfunction of the main electric power supply system (1, 10) which includes an industrial apparatus operated by cooperatively controlling an auxiliary machinery (2) operated by the electric power supplied from the main electric power supply system (1, 10), an auxiliary electric power supply (20) for storing the electric power, a charging circuit (21) for charging the electric power supplied from the main electric power supply (1) in the auxiliary electric power supply (20), a discharging circuit (22) for supplying the electric power charged in the auxiliary electric power supply (20) to the auxiliary machinery (2), and an emergency controlling circuit (40) for controlling the discharging circuit (22) so that the electric power from the auxiliary electric power supply (20) is supplied to the auxiliary machinery (2) at the time of the malfunction of the main electric power supply system (1, 10) and for controlling the operation of the auxiliary machinery (2) in response to the operational state of the industrial apparatus at the time of the malfunction of the main electric power supply system (1, 10).