This invention relates to a data transmitting apparatus and a data receiving apparatus, which multiplexes and transmits HD-SDI signals, and which receives the multiplexed and transmitted HD-SDI signals. The data transmitting apparatus is characterized by being equipped with a parallel data forming section which forms word string data De based on HD-SDI signals DHS of n channels, a data multiplexing section which obtains multiplex word string data Dm based on De, a multiple channel data forming section which forms bit string data DSX of m channels from Dm, a data multiplexing and P/S converting section which forms bit string data DTG based on DSX and in which a bit rate is set to 10 Gb/s or more, and an electric photo converting section which sends away DTG.