An unauthorized connection detecting device, which detects whether or not a power storage device is an unauthorized power storage device, includes: a communications unit receiving first charge/discharge information in which first identification information and first connection information are associated each other, the first identification information identifying an encryption key of the power storage device used for mutual authentication between a charge/discharge device and the power storage device, and the first connection information being on the power storage device and obtained when the power storage device is connected to the charge/discharge device; and an unauthorization detecting unit detecting whether or not the power storage device is the unauthorized power storage device, by determining, using the first identification information and the first connection information, whether or not two or more power storage devices associated with a single first identification information item are present.
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