A thumb-operated dial-type integrated switch for automobile use was developed, and the task completion time for this type of integrated switch was compared with that for a traditional integrated switch. The rotation torque of an encoder and the rotation diameter were selected as experimental parameters. An attempt was made to identify the optimal and recommended condition of rotation torque and diameter. It was demonstrated that the thumb-operated dial-type integrated switch lead to faster task completion time as compared with the traditional integrated switch. As for the thumb-operated dial-type integrated switch, the following combination of the rotation torque and the rotation diameter were not proper: diameter of 20mm for the rotation torque of 12.9mN・m and 9.2mN・m, and diameters of 20mm and 40mm for the rotation torque of 8.6 mN・m. It was also suggested that the optimal condition cannot be identified using the condition of the rotation force only, and that the optimal condition must be determined taking into account the combination of the rotation torque and the rotation diameter.