A display control system includes a mobile terminal device and an in-vehicle device. The mobile terminal device is configured to display an agent image by executing an agent program. The in-vehicle device is configured to display an agent image by executing an agent program. The in-vehicle device includes a detection unit and a display control unit. The detection unit is configured to detect the mobile terminal device as a result of receiving identification information from the mobile terminal device. The display control unit is configured to, when the mobile terminal device has been detected by the detection unit, cause the in-vehicle device to display the agent image. The mobile terminal device is configured to, when the display control unit causes the in-vehicle device to display the agent image, prohibit display of the agent image on the mobile terminal device.