A bit-likelihood calculating apparatus includes an initial-bit-likelihood calculating unit obtaining an inter-transmission-signal-point distance corresponding to N, a region number indicating a determination region of a transmission signal point nearest from data, and inter-nearest-point distance from a transmission signal point of initial bit=0 nearest to the data and a transmission signal point of initial bit=1 nearest to the data, and calculating likelihood of initial bit of the data serving as initial term of a recurrence formula for recursively calculating bit likelihood, an i-th-bit-likelihood calculating unit calculating, when N is 2 or larger, difference between inter-nearest-point distance with respect to (i−1)th bit and inter-nearest-point distance with respect to i-th bit and calculating likelihood of i-th bit of the data from likelihood of (i−1)th bit and the difference using the recurrence formula, and a processing-step control unit controlling calculation processing for bit likelihood based on N.
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