Abstract: An air-conditioning system operates in an automatic control mode when an auto-switch is on. When a rotary member which is manually rotated to set one air-conditioning factor is rotated while the auto-switch is on, the air-conditioning system operates in a manual control mode as far as the one air-conditioning factor. The rotary member can be rotated endlessly. When the rotary member is rotated from one angular position to another when the air-conditioning system is operating in the automatic control mode, the one air-conditioning factor is set to a mode or a value which is determined on the basis of the amount of rotation and the mode or the value to which it had been set when the rotary member was in the one angular position.