PURPOSE: To accurately discriminate the presence, or absence of a both-side carrying unit even in the case of setting the both-side carrying unit in the process, or supplying a power in the process by executing a self-diagnostic step for inspecting the internal function of the both-side carrying unit in accordance with the prescribed procedure when the both-side carrying unit is loaded, or when a current is supplied to the both- side carrying unit.

CONSTITUTION: When it is detected that the both-side carrying unit is loaded, the state of a driving system in the both-side carrying unit and the presence, or absence of a paper are checked by a self-diagnostic control part 111, then, the part 111 informs an engine control part 102 whether it is normal, or abnormal. First of all, the connection state of the both-side carrying unit is checked. Whether or not the unit is connected is checked through a communication channel between the engine control part 102 and the both-side carrying control part 109. When the connected state is confirmed, the presence, or absence of the paper in the both-side carrying unit is checked by the engine control part 102. In the case the in-machine paper is not present, the state of the driving system in the both-side carrying unit, for example, the state of a DC motor is checked at this time.