To provide a data transfer system with which retry transfer is efficiently performed without measuring the number of times of retry and the time.

Data transmitted from one bus [common bus (a)] to the other bus [common bus (b)] are successively stored in the buffer memory of a data buffer part 13, the data read out of the buffer memory are sent out as output data to the other bus, and the data buffer part 13 temporarily holds these output data. When a retry request is generated from the common bus (b), these held output data are written in the buffer memory again and the output data of retry object are read out of the buffer memory again and sent out to the common bus (b) so that the retry operation is performed.