Elements necessary for a digital television receiver are structured as blocks that are a plurality of digital signal processing blocks and a host arithmetic operation processing block. The blocks are connected through a general-purpose bus. Commands for controlling operations of the blocks and data of streams are transferred through the bus. An extension plug-in card for a new service can be attached and detached to/from the bus. The extension plug-in card has hardware that accomplishes an extension function and a script for commands of the hardware. When the extension plug-in card is attached to the bus through an interface, the script for the commands is automatically uploaded to the host arithmetic operation processing block side. The host arithmetic operation processing block can operate the extension plug-in card corresponding to the transferred script for the commands.