A guide system terminal device is provided to facilitate group operation vehicles. The guide system terminal device has a transceiver that receives the traveling environment information from another vehicle, such as for the turn signal, vehicle speed, running position, a road change judgment module that judges course changes by the other vehicle based on the traveling environment information of the other vehicle, and a user interface that outputs the judgment result obtained by road change judgment module. For example, the road change judgment module judges a left/right turn to have occurred when the blinker information acquired by turn signal sensor lasts longer than a prescribed time, and when the maximum value of the change in vehicle speed exceeds a prescribed level.