A first mobile terminal testing device 1 including plurality of pseudo base station units 12-0, 12-1 operating as LTE base stations of NSA, and second mobile terminal testing device 2 operating as 5G NR base stations of NSA are provided. Each of the pseudo base station units 12-0, 12-1 is associated with the second mobile terminal testing devices 2, 2. The second mobile terminal testing device 2 generates a 5G NR control signal when testing a mobile terminal 3 which supports for NSA. The generated 5G NR control signal is transmitted to the first mobile terminal testing device 1. The first mobile terminal testing device 1 transmits the received 5G NR control signal to the mobile terminal 3 by the LTE control signal using the pseudo base station unit 12 corresponding to the second mobile terminal testing device 2 which transmits the control signal.