PURPOSE: To constitute the computer system using an uninterruptible power supply whose maintainability is so improved that it is convenient for the operation of the computer system by constituting an interface which informs an operator of the abnormality of a power supply source, the battery use state, or the like.

CONSTITUTION: The microcomputer incorporating an uninterruptible power supply (UPS) 14 detects the AC input power state and the battery use state (including the timer management) and sets them as status flags, and an arithmetic processing mechanism 15 on the computer side recognizes them by status read to realize the guidance display on a work station (WS) 12 connected to the system by the interrupt control.