In a digital modulation method, a plurality of kinds of multiplexed blocks are generated by respectively multiplexing a plurality of kinds of t-bit initial data upon the leading edges of input blocks (before conversion), and the exclusive OR of the leading (t) bits of each multiplexed block and the (t) bits immediately after the leading (t) bits is calculated. Then, the (t) bits immediately after the leading (t) bits are replaced on the basis of the above resultant, and the exclusive OR of the replaced (t) bits and the (t) bits immediately after the replaced (t) bits is calculated. Thereafter, the (t) bits immediately after the calculated (t) bits are replaced on the basis of the resultant on the exclusive - OR calculation. Thereafter, the convolution is similarly executed and the DC components of the converted blocks generated by the convolution are calculated and the minimum converted block is selected by comparing the magnitudes of the absolute values of the DC components with each other and outputted.