PURPOSE: To enhance a correction efficiency by detecting out of synchronism before a burst error of transmission data is corrected in bit interleaving.

CONSTITUTION: In this embodiment, a data part 10 consists of four real data 11 comprising A0-A3,..., D0-D3 in 4-bits each and of four redundant data 12 comprising A4-A6,..., D4-D6 in 3-bits each. In a conventional method, only the data part 10 is sent in the order of transmission lines n=1-7 and a 1-bit error of any of 7-bit data A0-A6,..., D0-D6 is corrected. A synchronization check pattern 21 is added to the data part 10, which is sent in the order of transmission lines n=1-7. When out of synchronism takes place, a difference takes place in the lateral arrangement of bits 1 in the synchronization check pattern 21, then the arrangement of the data part 10 in which out of synchronism is corrected by adding or deleting bits to correct the difference is obtained and error correction by a conventional method is applied to the data arrangement.