PURPOSE: To record data with a high density, by reducing a maximum interval of magnetization inversion to facilitate clock regeneration, by converting specific code word and code sequence when prescribed bits of two code words based on the 3PM system are 0.

CONSTITUTION: In the modulation of data signals based on the 3PM system, when all bits from the second bit to the sixth bit of a code word A are 0 and the first bit and the second bit of a next code word B are 0, pattern 001001 is used as the code word instead of the code word A. When the second bit and the fifth bit of the code word A are 1 and 0 respectively and all bits from the first bit to the fourth bit of the code word B are 0, the sixth bit of the code word A is set to 1, and pattern 001000 is used as the code word instead of the code word B. Further, pattern 101 in a code sequence obtained by conversion is converted to pattern 010. For example, a modulating circuit (a) and a demodulating circuit (b) shown in figures are used to perform magnetic recording and reproducing in this manner.