A method for driving an information processing device which is adaptable to a wider variety of input methods is provided. The coordinates of an operating body at a starting point in the XYZ space and the coordinates of the operating body at an ending point in the XYZ space after a certain period of time are obtained, and the Z coordinate at the ending point and the movement distance on the X-Y plane in the certain period of time are calculated. Then, a signal is output only in the case where both the distance from an operating surface to the operating body in the vertical direction and the movement distance in the horizontal direction exceed the respective threshold values. In this manner, input operation can be performed by a three-dimensional motion, which includes movement of the operating body in the vertical direction as well as in the horizontal direction.