A vehicle charging system comprising an apparatus mounted on a vehicle for charging an on-vehicle battery from an external power supply with a charging plug connected to the vehicle, comprising: a communication device that is configured to perform communication with a charging facility providing the external power supply with the charging plug connected and locked to the vehicle, and to prohibit disconnection of the communication when an unlocking operation to unlock the charging plug is executed during charging from the external power supply to the on-vehicle battery, wherein the prohibition of disconnection of the communication includes stopping communication in an Application layer in an OSI reference model based on which the communication is performed, while retaining an established state of a communication session in a Session layer and layers therebelow, wherein the communication device is configured to perform communication with the charging facility in an Application layer in the OSI reference model based on which the communication is performed after performing communication for user verification and authentication with the charging facility when the charging plug is connected and locked to the vehicle, the communication device is configured to stop the communication in the Application layer while retaining the established communication session in the Session layer and layers therebelow until a time period for which the operation of the unlocking button is continued exceeds a predetermined time period, the communication device is configured to resume the communication in the Application layer without performing the communication for user verification and authentication when an unlocking operation to unlock the charging plug is executed during charging from the external power supply to the on-vehicle battery but the unlocking operation is not being continued for the predetermined time period, and the communication device is configured to stop also the communication session in the Session layer and layers therebelow if the time period for which the operation of the unlocking button is continued is greater than the predetermined time period during charging from the external power supply to the on-vehicle battery. a communication device that is configured to perform communication with a charging facility providing the external power supply with the charging plug connected and locked to the vehicle, and to prohibit disconnection of the communication when an unlocking operation to unlock the charging plug is executed during charging from the external power supply to the on-vehicle battery, wherein the prohibition of disconnection of the communication includes stopping communication in an Application layer in an OSI reference model based on which the communication is performed, while retaining an established state of a communication session in a Session layer and layers therebelow, wherein the communication device is configured to perform communication with the charging facility in an Application layer in the OSI reference model based on which the communication is performed after performing communication for user verification and authentication with the charging facility when the charging plug is connected and locked to the vehicle, the communication device is configured to stop the communication in the Application layer while retaining the established communication session in the Session layer and layers therebelow until a time period for which the operation of the unlocking button is continued exceeds a predetermined time period, the communication device is configured to resume the communication in the Application layer without performing the communication for user verification and authentication when an unlocking operation to unlock the charging plug is executed during charging from the external power supply to the on-vehicle battery but the unlocking operation is not being continued for the predetermined time period, and the communication device is configured to stop also the communication session in the Session layer and layers therebelow if the time period for which the operation of the unlocking button is continued is greater than the predetermined time period during charging from the external power supply to the on-vehicle battery.