The determination portion 34 determines whether the connection relationship between the expansion device 2 and the power supply portion is correct or incorrect, based on the connection relationship identified by the connection identifying portion 32 and the expansion device 2 identified by the device identifying portion 33. In short, depending on the type of expansion devices 2, due to power consumption, etc., the expansion devices 2 should be connected to the expansion power supply portion 19 instead of the main body power supply portion 18, or should be connected to the main body power supply portion 18 instead of the expansion power supply portion 19. Thus, in the determination portion 34, when each expansion device 2 is connected to the power supply portion to be connected (the main body power supply portion 18 or the expansion power supply portion 19), it is determined that the connection relationship is correct. For example, in an example of FIG. 3, the expansion device 202 should be connected to the main body power supply portion 18, and the expansion device 203 should be connected to the expansion power supply portion 19. The expansion device 2 is identified, which determines the connection relationship between the identified expansion device 2 and an appropriate power supply portion depending on such expansion device 2. Therefore, when the connection relationship identified in the connection identifying portion 32 matches such appropriate connection relationship, the determination portion 34 determines that the connection relationship is correct.