PURPOSE: To convert a speed of parallel data simultaneously altogether even in the case of data of plural channels by arranging once data entered in irregular timings.

CONSTITUTION: In the serial parallel data conversion method receiving serial data with a block of a prescribed size compressed and speed-converted at a high speed and applying speed conversion of received data into a speed of data before compression, packet data entered irregularly are arranged at an equal interval by a 1st SRAM 11 and a data conversion circuit 12 converts the data into parallel data. The arranged data are delayed by the number of bits being a difference between a value obtained by dividing the number of bits of the block by the number of entire channels and the number of bits in a time slot in a 2nd SRAM 13 and the result is sequentially outputted to a 3rd SRAM 14. Furthermore, the result is fed back to apply speed conversion to prescribed bits of the head of data corresponding to the number of delayed bits sequentially.