An image processor keeps itself capable of executing a communication process with an external apparatus even in an energy-saving state, and offers a job reservation function while reducing power consumption as much as possible. The image processor has an energization switching circuit that makes switchover separately in energizing/deenergizing each of a plurality of function blocks, which execute a job, independent of energization of a Network Interface Card (NIC). The NIC has functions of counting the present time, obtaining a scheduled time and reserved job information on a reserved job to be executed at the scheduled time, identifying the reserved job to be started for execution on the basis of a counted time and the scheduled time included in the reserved job information, and starting up a function block needed for execution of the identified reserved job through control over the energization switching circuit.