A broadcast signal receiving apparatus receives a plurality of transport streams and uses conditional access provided by an external adapter. The broadcast signal receiving apparatus includes a pre-processor operable to extract a part of information, by elementary stream unit, from each of the plurality of transport streams by receiving a filtering condition from the external adapter and performing filtering on the plurality of transport streams according to the filtering condition. The broadcast signal receiving apparatus also includes a multiplexer, an output interface, an input interface, and a demultiplexer. The external adapter is detachable from the broadcast signal receiving apparatus, and includes a conditional access descrambler that descrambles transport stream packets in the multiplexed data that are protected by conditional access with a packet identifier specified by the controller in the broadcast signal receiving apparatus.