In the present embodiment, as one example, the expansion power supply portion 19 is electrically connected to an AC plug 191 (see FIG. 3) and has an AC/DC converter that converts an AC 100V (or 200V) voltage applied to the AC plug 191 into a DC 24V voltage. In other words, in a state in which the AC plug 191 is connected to an outlet, AC power is applied from an AC power source such as a grid power supply to the expansion power supply portion 19. Therefore, the expansion power supply portion 19 uses such AC power to generate DC power. In the present embodiment, the expansion power supply portion 19 that is, for example, a power supply circuit using a switching method, can control operations, from the outside by using a remote signal which will be described later.

FIG. 3 schematically illustrates a connection relationship between the main body 1 and the plurality of expansion devices 201 to 203, and a connection relationship of a power supply passage to be a strong-current system. FIG. 3 does not illustrate the ADF 11, the image reading portion 12, the image forming portion 13, the sheet feed portion 14, the operation display portion 15, and each functional portion (such as a fluctuation generating portion 31, etc.) included in the main body control portion 16, and each functional portion (such as a detection portion 36, etc.) included in the expansion control portion 22.