To enable transmitting plural kinds of MPEG picture information data by obtaining 8-bit word string data based on plural kinds of picture information data, converting the bit in 8 bit to 10 bit word string data and inserting an additional word data group including 10-bit synchronous data having a previously set code at prescribed interval.

Eight-channel MPEG picture information data A0-A7 are supplied to a 10-bit word string data generating part 11 and supplied to an 8B-10B conversion part 12, in a state where bit synchronization is mutually obtained. The bits are converted into 10-bit word string data, DX (10) is obtained and it is supplied to a speed converting and synchronous data inserting part 22. The part 22 executes word rate conversion with respect to the 10-word string data DX (10), inserts an additional word data group DWP or DWN at previously set prescribed word interval and generates a 10-bit word string DZ (10).