A knob device is applicable to a touch panel. The knob device includes a knob cover, a plurality of sensing pads and a rotation sensing element. The plurality of sensing pads are fixedly arranged on the touch panel. A gap is form between two sensing pads. The plurality of sensing pads and gaps are distributed in a ring area around a center of an orthographic projection of the knob cover. The rotation sensing element is connected to the knob cover. When the knob cover is turned to be rotated, the rotation sensing element is rotated synchronously. When a user touches the knob device and the rotation sensing element overlaps one of the plurality of sensing pads, the touch panel generates a rotation sensing signal in response to a location of the rotation sensing element.