This paper proposes an automatic driving system for lane change maneuver on highway. The automatic driving system is based on a reference driver model which employs on-board vehicle external sensing signals and estimates the initiation timing and the magnitude of longitudinal and lateral accelerations as reference signals. The patterns of reference accelerations are determined by modeling the expert drivers’ experimental maneuvers. The proposed automatic driving system is tested on a driving simulator (DS) of Tokyo University of Agriculture and Technology (TUAT) by applying control systems which convert the reference accelerations to vehicle control input such as the accelerator pedal displacement and the steering wheel angle. The results by the automatic driving show good consistency with the results obtained by the expert driver experiments. The effectiveness of the proposed automatic driving system is verified by changing the velocity difference between the lanes to show that the system can handle various lane change situations.