PURPOSE: To reduce jitter at the time of recording and reproducing in writing data on a magnetooptic disk, for example.

CONSTITUTION: A coding modulation processing circuit 11 conducts coding modulation of the data to be recorded, and thus processed data is supplied to a data conversion and processing circuit 12. The circuit 12 divides each channel bit after coding modulation in n (n is an integer of two or more) based on the dividing parameter supplied from a dividing parameter memory setting circuit 14, and, at the same time, applies data conversion to the above n-divided channel bit in compliance with a specified conversion pattern supplied from a conversion pattern storing circuit 15. And the output of the data conversion circuit 12 is supplied to a data recording circuit 16 to write data on the magnetooptic disk D used for a recording medium.