To prevent the complete omission of a log due to log information which is destroyed since it cannot be transmitted, when the communication log information of a plurality of layers is transmitted and a log is displayed at a transmission destination. A test device 10 includes a log header generating unit 151 that generates a log header including layer identification information and time information, a log data generating unit 152 that generates log data including communication data, a test-device-side transmitting unit 17 that transmits the log header and the log data to a display device 30, and a priority control unit 19 that performs control such that the log header is transmitted prior to the log data. A display control unit 35 of the display device 30 displays a log such that the log header is associated with the log data.