To obtain a bit-likelihood calculating apparatus that has fewer approximation errors and is capable of reducing the computational complexity and the amount of memory. The bit-likelihood calculating apparatus includes an initial-bit-likelihood calculating unit 210 obtaining an inter-transmission-signal-point distance corresponding to a value of 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 230 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 220 controlling calculation processing for bit likelihood by the i-th-bit-likelihood calculating unit 230 based on the value of N.