A server for providing a plurality of vehicles (1 to 4) including a target vehicle with charging information for external charging, wherein each of the plurality of vehicles (1 to 4) including the target vehicle is mounted with a power storage device, the server comprising: a communication device configured to communicate with the plurality of vehicles; and a circuitry configured to generate the charging information, wherein the circuitry is configured to: obtain an accessible range for each of the plurality of vehicles (1 to 4) to extract at least one charger within the obtained accessible range, the accessible range being determined by power stored in the power storage device of each of the plurality of vehicles (1 to 4)and a current location of each of the plurality of vehicles (1 to 4); calculate a total number of chargers within the accessible range of each of the plurality of vehicles (1 to 4) to calculate a reduced number so that the greater the total number of chargers is, the less the reduced number is, the reduced number representing a likelihood that the vehicle would arrive at each of the chargers; calculate an effective number of vehicles which may use each of the at least one charger to conduct external charging, by summing reduced numbers of each of the at least one charger; and calculate an index indicating a potential demand for external charging at each of the at least one charger based on the effective number, and send the index to the target vehicle. a communication device configured to communicate with the plurality of vehicles; and a circuitry configured to generate the charging information, wherein the circuitry is configured to: obtain an accessible range for each of the plurality of vehicles (1 to 4) to extract at least one charger within the obtained accessible range, the accessible range being determined by power stored in the power storage device of each of the plurality of vehicles (1 to 4)and a current location of each of the plurality of vehicles (1 to 4); calculate a total number of chargers within the accessible range of each of the plurality of vehicles (1 to 4) to calculate a reduced number so that the greater the total number of chargers is, the less the reduced number is, the reduced number representing a likelihood that the vehicle would arrive at each of the chargers; calculate an effective number of vehicles which may use each of the at least one charger to conduct external charging, by summing reduced numbers of each of the at least one charger; and calculate an index indicating a potential demand for external charging at each of the at least one charger based on the effective number, and send the index to the target vehicle. obtain an accessible range for each of the plurality of vehicles (1 to 4) to extract at least one charger within the obtained accessible range, the accessible range being determined by power stored in the power storage device of each of the plurality of vehicles (1 to 4)and a current location of each of the plurality of vehicles (1 to 4); calculate a total number of chargers within the accessible range of each of the plurality of vehicles (1 to 4) to calculate a reduced number so that the greater the total number of chargers is, the less the reduced number is, the reduced number representing a likelihood that the vehicle would arrive at each of the chargers; calculate an effective number of vehicles which may use each of the at least one charger to conduct external charging, by summing reduced numbers of each of the at least one charger; and calculate an index indicating a potential demand for external charging at each of the at least one charger based on the effective number, and send the index to the target vehicle.