A bit-likelihood calculating apparatus that performs a bit likelihood calculation on data obtained by receiving a modulation signal mapped by N (N is an integer equal to or larger than 1) bit per symbol, the apparatus comprising: an initial-bit-likelihood calculating unit that obtains 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 the data, and an inter-nearest-point distance from a transmission signal point of an initial bit = 0 nearest to the data and a transmission signal point of an initial bit = 1 nearest to the data, and calculates likelihood of an initial bit of the data serving as an initial term of a recurrence formula for recursively calculating bit likelihood; an i-th-bit-likelihood calculating unit that, when N is equal to or larger than 2, calculates a difference between an inter-nearest-point distance with respect to an (i-1)th bit and an inter-nearest-point distance with respect to an i-th bit, and calculates likelihood of the i-th bit of the data from likelihood of the (i-1)th bit and the difference using the recurrence formula; and a processing-step control unit that controls calculation processing for bit likelihood by the i-th-bit-likelihood calculating unit on a basis of the value of N, characterised in that the recurrence formula is as follows: LLR S i + 1 = d i + Δ i 2 l l − 2 N / 2 − 1 A + d i + Δ i A + A − r l = d i + Δ i β i + Δ i A = LLR S i + Δ i d i A + β i + Δ i A, wherein LLRS i +1 is the likelihood of the (i + 1) - th bit, LLR S 0 = d 0 2 l l − 2 N / 2 − 1 A + d 0 A + A − r l, d i represents the inter-nearest-point distance, which is a shortest distance to a region where the hard decision value of the i-th bit is inverted, Δ i = d i + 1 − d i, l I is the region number on an I axis or on a Q axis, r I represents an I component or Q component of the reception data, A represents a half value of the inter-transmission-signal-point distance of two adjacent signal points, with the range of each region being 2A, β i = 2 I l − 2 N / 2 − 1 A + d i A + A − r l, and β i + 1 = β i + Δ i A. an initial-bit-likelihood calculating unit that obtains 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 the data, and an inter-nearest-point distance from a transmission signal point of an initial bit = 0 nearest to the data and a transmission signal point of an initial bit = 1 nearest to the data, and calculates likelihood of an initial bit of the data serving as an initial term of a recurrence formula for recursively calculating bit likelihood; an i-th-bit-likelihood calculating unit that, when N is equal to or larger than 2, calculates a difference between an inter-nearest-point distance with respect to an (i-1)th bit and an inter-nearest-point distance with respect to an i-th bit, and calculates likelihood of the i-th bit of the data from likelihood of the (i-1)th bit and the difference using the recurrence formula; and a processing-step control unit that controls calculation processing for bit likelihood by the i-th-bit-likelihood calculating unit on a basis of the value of N, characterised in that the recurrence formula is as follows: LLR S i + 1 = d i + Δ i 2 l l − 2 N / 2 − 1 A + d i + Δ i A + A − r l = d i + Δ i β i + Δ i A = LLR S i + Δ i d i A + β i + Δ i A, wherein LLRS i +1 is the likelihood of the (i + 1) - th bit, LLR S 0 = d 0 2 l l − 2 N / 2 − 1 A + d 0 A + A − r l, d i represents the inter-nearest-point distance, which is a shortest distance to a region where the hard decision value of the i-th bit is inverted, Δ i = d i + 1 − d i, l I is the region number on an I axis or on a Q axis, r I represents an I component or Q component of the reception data, A represents a half value of the inter-transmission-signal-point distance of two adjacent signal points, with the range of each region being 2A, β i = 2 I l − 2 N / 2 − 1 A + d i A + A − r l, and β i + 1 = β i + Δ i A. l I is the region number on an I axis or on a Q axis, r I represents an I component or Q component of the reception data, A represents a half value of the inter-transmission-signal-point distance of two adjacent signal points, with the range of each region being 2A,