Two input-side data transmission paths are provided in parallel with each other, and a competition detecting part detects the time difference between times of arrival of transmission signals supplied to the respective data transmission paths for stopping the data arriving with a delay on the data transmission path therefor if the time difference is within a constant range. Thereby, the time difference is rendered to be outside of the constant range. A word number counting part counts the word numbers of the data transmitted to the data transmission paths, and an arbitration control part supplies transmission authorizing signals to the respective input-side data transmission paths for transmitting the data of the counted word numbers to an output-side data transmission path. The two input-side data transmission paths are provided with buffer mechanisms for changing the amounts of data delay in response to the degree of data occupancy.