In a digital copier system wherein a plurality of applications share a plurality of resources, a system controller executes exclusive control with duplex copy unit requests sent from a plurality of applications, thereby allowing only one application to use a duplex copy unit. This guarantees the consistency of the system by eliminating problems attributable to a decision on the duplex copy unit which differs from one application to another application. Further, when a paper or papers are left on the unit after a certain application has occupied the unit for more than a predetermined period of time, the system forcibly discharges them from the unit and causes the application to release the right to use the unit.