An unauthorized connection detecting device which is configured to detect whether or not a charge/discharge device connected to the unauthorized connection detecting device is an unauthorized charge/discharge device, the charge/discharge device being included in charge/discharge devices for charging or discharging a secondary battery with power, and the unauthorized connection detecting device comprising: a time information obtaining unit configured to obtain, as time information, information from a first charge/discharge device when the unauthorized connection detecting device is connected to the first charge/discharge device, the information indicating at least one of (i) an issuing date of a first certificate which is a public key certificate held by the first charge/discharge device for authentication and (ii) an issuing date of a certificate revocation list including revoked public key certificates and held by the first charge/discharge device, and the first charge/discharge device being included in the charge/discharge devices; an expiration date obtaining unit configured to obtain expiration date information from a second charge/discharge device when the unauthorized connection detecting device is disconnected from the first charge/discharge device and is connected to the second charge/discharge device, the expiration date information indicating an expiration date of a second certificate which is a public key certificate held by the second charge/discharge device for authentication, and the second charge/discharge device being included in the charge/discharge devices, wherein the second charge/discharge device is different from the first charge/discharge device; and an unauthorization detecting unit configured to detect whether or not the second charge/discharge device is the unauthorized charge/discharge device by comparing the time information of the first charge/discharge device with the expiration date information of the second charge/discharge device. a time information obtaining unit configured to obtain, as time information, information from a first charge/discharge device when the unauthorized connection detecting device is connected to the first charge/discharge device, the information indicating at least one of (i) an issuing date of a first certificate which is a public key certificate held by the first charge/discharge device for authentication and (ii) an issuing date of a certificate revocation list including revoked public key certificates and held by the first charge/discharge device, and the first charge/discharge device being included in the charge/discharge devices; an expiration date obtaining unit configured to obtain expiration date information from a second charge/discharge device when the unauthorized connection detecting device is disconnected from the first charge/discharge device and is connected to the second charge/discharge device, the expiration date information indicating an expiration date of a second certificate which is a public key certificate held by the second charge/discharge device for authentication, and the second charge/discharge device being included in the charge/discharge devices, wherein the second charge/discharge device is different from the first charge/discharge device; and an unauthorization detecting unit configured to detect whether or not the second charge/discharge device is the unauthorized charge/discharge device by comparing the time information of the first charge/discharge device with the expiration date information of the second charge/discharge device.