Elements necessary for a digital television receiver are structured as 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 a stream are transferred through the bus. When an encryption encoder/decode is disposed in each block, contents transferred through the bus can be protected. When an encryption encoder/decode circuit is disposed in an interface to which an extension plug-in card is attached, contents that are output from the interface can be protected.