A server downloads data to a mobile station mounted in a vehicle through a roadside device using dedicated short range communication (DSRC). The server is capable of computing downloading transmission rate from the roadside device to the mobile station and maximum speed of the vehicle that enables completion of the downloading of the data to the mobile station. The maximum speed is computed based on the computed downloading transmission rate, a communication area of the roadside device, and size of the data. The server is further capable of notifying the maximum speed to the mobile station. By contrast, the mobile station is capable of transmitting information relating to the data to the server, receiving the data to be downloaded in the communication area of the roadside device, and notifying the maximum speed received from the server to a crew of the vehicle.