A transfer path between a sensor and a data processing server is partitioned into at least a first transfer path between the sensor and a first relay device, a second transfer path from the first relay device to a second relay device that transfers the data transmitted from the first sensor, and a third transfer path between the second relay device and the data processing server. A data transfer between each of the sensors and the data processing server is implemented by respectively controlling a pair of the first transfer path and the second transfer path, and a pair of the second transfer path and the third transfer path.