Abstract: An image recording apparatus consists of a control system including a CPU, an image input terminal, an image processing system, an image output terminal, and a user interface. An I/O controller is provided in each of the above units. During the power-on sequence of the apparatus, the CPU executes an interrupt test for checking whether interrupt processes of the CPU with respect to sync signals are performed correctly, and an I/O port operation test for confirming that an I/O port of each I/O controller functions correctly. When a prescribed button is pressed at the user interface, the CPU enters a diagnostic copy job mode, in which copies are actually produced in the same manner as in a normal copy mode to identify a unit in trouble.