The code conversion method of the present invention includes the steps of: scrambling an input main data unit based on any of plural types of pseudo-random number sequences; modulating the scrambled main data unit based on any of plural types of modulation data; producing an output main data unit from the modulated main data unit; obtaining a calculated value representing a difference between a number of 0 bits and a number of 1 bits included in the output main data unit; and selecting any of the modulation data dependent upon the calculated value. The code conversion method of the present invention is characterized by further including the steps of: determining whether or not a variation of the calculated value has exceeded a predetermined threshold value; newly selecting another pseudo-random number sequence used for the step of scrambling if it is determined that the variation of the calculated value has exceeded the predetermined threshold value; and re-scrambling the input main data unit based on the newly selected pseudo-random number sequence.