PURPOSE: To make the timing of indication different in accordance with the kind and/or the degree of importance of a generated error.

CONSTITUTION: When an error is detected by a printer controller 22 and an engine control unit 24 during warming-up, the kind of detected error is recognized and when the error is in a kind that does not permit the continuation of warming-up, an error message is indicated immediately and the warming-up is stopped. When the error is in a kind that permits the continuation of the warming-up, the indication of warming-up and the indication of error message are indicated alternately and repeatedly. According to this method, emergency coping with the generated error is permitted and an indication panel can be used effectively.