In an input device, a controller for controlling an input portion and acquiring data is connected to a bus. The bus can be connected with an external expansion device via an expansion connector. The connection of the bus from the expansion connector to the controller is switched on and off by a switcher. Data acquired from a sensor having a function equivalent to that of the external expansion device is transmitted to the controller via the bus by a sensor controller which is connected to each of a side of the controller and a side of the expansion connector of the bus without interposing the switcher. The sensor controller switches the connection of the switcher off when an access to itself is made from the controller.