PURPOSE: To ensure the conversion of data from a serial data into a parallel data by bringing the operating frequency in each shift register to obtain plural 1st parallel data into 1/n of the frequency of the serial data without causing the synchronizing state with respect to an incoming serial data.

CONSTITUTION: The operating frequency in respective shift registers 4, 5 to obtain plural 1st parallel data 107-110, 111-114 is brought into 1/n such as 1/2 of the frequency of the serial data without losing the synchronizing state with respect to the incoming serial data 104. Thus, the shift registers 4, 5 are not inoperative due to the increase in the transmission speed of the serial data 104, that is, the increase in the readout frequency. Thus, the conversion from the serial data 104 into the parallel data 115a or 116a is ensured without being affected by the increase in the transmission speed.