PURPOSE: To eliminate the need for idle reading of a data and to avoid duplicated serial processing for a parallel data by transferring the data from the 1st to the 2nd storage means only when a new data is stored in the 1st storage means.

CONSTITUTION: RS-FFs133, 134 and a 4-input AND gate 135 are added. The RS-FF133 is provided corresponding to D-FF 111∼11N. Thus, an empty signal indicating the possibility of entering a new parallel data to the D-FF 111∼11N is outputted from an empty signal output terminal 162. On the other hand, the RS-FF 134 is provided corresponding to the 2nd D-FFs 121∼12N. Thus, a ready signal indicating the possibility to extract a serially processed data is outputted from a ready signal output terminal 143. Moreover, the output of the AND gate 135 is fed to a clock terminal of the D-FFs 121∼12N.