1. A digital broadcast receiver comprising: a monitor for displaying, as an image, video data and caption data each extracted from digital broadcast signals received; a speaker for outputting, as audio, audio data extracted from the received digital broadcast signals; caption selecting means for selecting caption data representing captions in a certain language from the extracted caption data on the basis of a language designated by a user for caption output so as to cause the monitor to display captions based on the selected caption data; audio selecting means for selecting audio data representing audio in a certain language from the extracted audio data on the basis of a language designated by a user for audio output so as to cause the speaker to output audio based on the selected audio data; and designated language setting means for setting both the language designated for caption output and the language designated for audio output as a designated language that is unified, wherein the caption selecting means compares the designated language set by the designated language setting means with languages in which captions are available from the caption data extracted from the digital broadcast signals, and if the designated language is included in the languages in which the captions are available from the extracted caption data, the caption selecting means selects caption data representing captions in the designated language; wherein the audio selecting means compares the designated language set by the designated language setting means with languages in which audio is available from the audio data extracted from the digital broadcast signals, and if the designated language is included in the languages in which the audio is available from the extracted audio data, the audio selecting means selects audio data representing audio in the designated language, wherein the designated language setting means allows setting of two or more designated languages having different priorities, wherein the caption selecting means compares the designated languages set by the designated language setting means with languages in which captions are available from the caption data extracted from the digital broadcast signals, and if some or all of the designated languages are included in the languages in which the captions are available, the caption selecting means selects caption data representing captions in one of the some or all of the designated languages that has a highest priority, and if none of the designated languages is included in the languages in which the captions are available, the caption selecting means selects caption data representing captions in a most universal language among the languages in which the captions are available; wherein the audio selecting means compares the designated languages, which are set by the designated language setting means, with languages in which audio is available from the audio data extracted from the digital broadcast signals, and if some or all of the designated languages are included in the languages in which the audio is available, the audio selecting means selects audio data representing audio in one of the some or all of the designated languages that has a highest priority, and if none of the designated languages is included in the languages in which the audio is available, the audio selecting means selects audio data representing audio in a most universal language among the languages in which the audio is available; and wherein the caption selecting means and the audio selecting means determine a match between the designated languages and the languages in which the captions or audio is available from the extracted caption or audio data as well as universality of a language based on numbers of language codes.