To provide a communication unit that can prevent increase in bit errors and to save on required transmission power.

A digital modulation system and a coding rate of an error correction code of a modulation section 102 are varied adaptively with setting information, extracted by a slot decomposition section 116 and set by each subcarrier or each segment. A demodulation section 115 uses the metric value of a Viterbi decoder to decide the modulation system and the coding rate, gives the setting information to a slot synthesis section 101, where a slot is formed with a modulation data bit and the result is given to the modulation section 102. On the basis of time fluctuations of the metric value and its integrated value, an optimum coding rate and an optimum modulation system can be set, while being adapted to a state of a propagation path corresponding to each subcarrier or each segment.