When an engine detects changes in condition such as a power-OFF operation, an out-of-paper state, or the like, it sends a condition change signal indicating that the condition has changed to an engine control unit. The engine control unit inquires of the engine as to the contents of the changes in condition using a command signal so as to examine the cause of the changes in condition. When a power supply is scheduled to be turned off, a message indicating it is supplied to a host computer that uses the printer, or job conditions are saved, and the host apparatus is informed of the saved job conditions after the power supply is turned on again. In the case of the out-of-paper state as well, a message indicating it is supplied to the host computer that uses the printer. The items to be informed can be selected from the host computer.