In the present embodiment, signals are transmitted and received between the main body 1 and the expansion device 2 through communication between the main body control portion 16 and the expansion control portion 22. Signals are transmitted and received among the plurality of expansion devices 2 through communication between the expansion control portions 22. In addition, in the present embodiment, the expansion devices 202, 203 (grandchild enhancement) are connected to the main body 1 via the expansion device 201 (child enhancement). Then, for the plurality of expansion devices 201 to 203, information for identifying the target expansion device 2 and information for identifying the connection relationship between the target expansion device 2 and the power supply portion are aggregated in the expansion device 201 and transmitted to the main body 1. That is, the expansion device 201 functions as an aggregator for the plurality of expansion devices 201 to 203.
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