Apparatus for transmitting data

PURPOSE: A data transmission apparatus is provided to convert digital AV data into a TP(Transport Packet) stream with an SD(Standard Definition) level and transmit the converted TP stream to a portable video device. CONSTITUTION: A decoder(200) decodes a TP stream with an HD(High Definition) level, converts the TP stream into digital AV data, and outputs the digital AV data. An AV processor(210) converts the output signal of the decoder into AV data with an SD level, and outputs the AV data with the SD level. An encoder(220) encodes the AV data outputted from the AV processor, and generates a TP stream. A wireless transmission unit(230) transmits the TP stream generated by the encoder to a portable video device.