An electronic control system comprising: a reconfigurable circuit device including a circuit unit including a reconfigurable circuit and a setting storage unit configured to store configuration information of the circuit unit; an acquisition unit configured to acquire difference information regarding a change part of a circuit element in the circuit unit; and a data conversion unit configured to update the configuration information based on the difference information, and further comprising a non-volatile storage unit configured to store the configuration information stored in the setting storage unit, wherein the data conversion unit is configured to update the configuration information stored in the non-volatile storage unit based on the difference information acquired by the acquisition unit, wherein the data conversion unit includes an address calculation unit configured to calculate an address of the non-volatile storage unit in which setting information of the circuit element is stored, based on identification information of the circuit element, and a setting information storing unit configured to store the setting information of the circuit element in an area corresponding to the address in the non-volatile storage unit, wherein the acquisition unit is configured to store the acquired difference information in the non-volatile storage unit, and the electronic control system further includes a diagnostic unit (71, 74) configured to diagnose whether or not all pieces of the setting information in the difference information is reflected in the configuration information of the non-volatile storage unit, and a reconfiguration control unit configured to store only predetermined configuration information that does not cause an abnormal operation among pieces of the configuration information stored in the non-volatile storage unit, in the setting storage unit in a case where all the pieces of the setting information in the difference information is not reflected in the configuration information of the non-volatile storage unit during circuit reconfiguration of the circuit unit in the reconfigurable circuit device, wherein the data conversion unit is configured to reflect, in a case where the diagnostic unit diagnoses that all the pieces of the setting information in the difference information are not reflected in the configuration information of the non-volatile storage unit, the setting information of the difference information, which has not been reflected, in the configuration information of the non-volatile storage unit. a reconfigurable circuit device including a circuit unit including a reconfigurable circuit and a setting storage unit configured to store configuration information of the circuit unit; an acquisition unit configured to acquire difference information regarding a change part of a circuit element in the circuit unit; and a data conversion unit configured to update the configuration information based on the difference information, and further comprising a non-volatile storage unit configured to store the configuration information stored in the setting storage unit, wherein the data conversion unit is configured to update the configuration information stored in the non-volatile storage unit based on the difference information acquired by the acquisition unit, wherein the data conversion unit includes an address calculation unit configured to calculate an address of the non-volatile storage unit in which setting information of the circuit element is stored, based on identification information of the circuit element, and a setting information storing unit configured to store the setting information of the circuit element in an area corresponding to the address in the non-volatile storage unit, wherein the acquisition unit is configured to store the acquired difference information in the non-volatile storage unit, and the electronic control system further includes a diagnostic unit (71, 74) configured to diagnose whether or not all pieces of the setting information in the difference information is reflected in the configuration information of the non-volatile storage unit, and a reconfiguration control unit configured to store only predetermined configuration information that does not cause an abnormal operation among pieces of the configuration information stored in the non-volatile storage unit, in the setting storage unit in a case where all the pieces of the setting information in the difference information is not reflected in the configuration information of the non-volatile storage unit during circuit reconfiguration of the circuit unit in the reconfigurable circuit device, wherein the data conversion unit is configured to reflect, in a case where the diagnostic unit diagnoses that all the pieces of the setting information in the difference information are not reflected in the configuration information of the non-volatile storage unit, the setting information of the difference information, which has not been reflected, in the configuration information of the non-volatile storage unit.