An input device for controlling multiple computers includes a storing unit, a sensing unit, a controlling unit, and a transmitting unit. The controlling unit calculates a moving direction and a displacement value of the input device according to the sensing unit to determine one of the computers which the input device is in control of and generates an input command for it. The input command includes identification of the controlled computer and is transmitted to multiple computers. The computer corresponding to the identification performs the input command. The moving direction corresponds to a pointer direction of the computer. The controlling unit accumulates the displacement value to be a first accumulated displacement value when the input device moves toward to a first pointer direction. When the first accumulated displacement value is larger than a threshold value, the controlling unit switches the input device to control another one of computers.