A voice processing device comprising: a first distribution generation unit that approximates a distribution of feature information representative of voice of a first speaker per a unit interval thereof as a mixed normal distribution which is a mixture of a plurality of first normal distributions (NS 1 to NS Q), the plurality of first normal distributions (NS 1 to NS Q) corresponding to a plurality of different phones; a second distribution generation unit that approximates a distribution of feature information representative of voice of a second speaker per a unit interval thereof as a mixed normal distribution which is a mixture of a plurality of second normal distributions (NT 1 to NT Q) corresponding to a plurality of different phones; wherein the voice processing device is characterized in that it is further comprising: a function generation unit that generates, for each phone, a conversion function (F 1 to F Q) for converting the feature information of voice of the first speaker to the feature information of voice of the second speaker based on respective statistics of the first normal distribution and the second normal distribution that correspond to the phone, wherein the conversion function for a qth phone (q = 1-Q) among a plurality of Q phones includes, using an average μ q X and an auto-covariance Σ q XX as statistics of the first normal distribution corresponding to the qth phone, an average μ q Y and an auto-covariance Σ q YY of the second normal distribution corresponding to the qth phone, and feature information X of voice of the first speaker, the following Equation: μ q Y + ∑ q YY ∑ q XX - 1 ⁢ X - μ q X or the following Equation: μ q Y + ε ⁢ ∑ q YY ∑ q XX - 1 ⁢ X - μ q X wherein ε is an adjusting coefficient (0<ε<1). a first distribution generation unit that approximates a distribution of feature information representative of voice of a first speaker per a unit interval thereof as a mixed normal distribution which is a mixture of a plurality of first normal distributions (NS 1 to NS Q), the plurality of first normal distributions (NS 1 to NS Q) corresponding to a plurality of different phones; a second distribution generation unit that approximates a distribution of feature information representative of voice of a second speaker per a unit interval thereof as a mixed normal distribution which is a mixture of a plurality of second normal distributions (NT 1 to NT Q) corresponding to a plurality of different phones; wherein the voice processing device is characterized in that it is further comprising: a function generation unit that generates, for each phone, a conversion function (F 1 to F Q) for converting the feature information of voice of the first speaker to the feature information of voice of the second speaker based on respective statistics of the first normal distribution and the second normal distribution that correspond to the phone, wherein the conversion function for a qth phone (q = 1-Q) among a plurality of Q phones includes, using an average μ q X and an auto-covariance Σ q XX as statistics of the first normal distribution corresponding to the qth phone, an average μ q Y and an auto-covariance Σ q YY of the second normal distribution corresponding to the qth phone, and feature information X of voice of the first speaker, the following Equation: μ q Y + ∑ q YY ∑ q XX - 1 ⁢ X - μ q X or the following Equation: μ q Y + ε ⁢ ∑ q YY ∑ q XX - 1 ⁢ X - μ q X wherein ε is an adjusting coefficient (0<ε<1). a function generation unit that generates, for each phone, a conversion function (F 1 to F Q) for converting the feature information of voice of the first speaker to the feature information of voice of the second speaker based on respective statistics of the first normal distribution and the second normal distribution that correspond to the phone, wherein the conversion function for a qth phone (q = 1-Q) among a plurality of Q phones includes, using an average μ q X and an auto-covariance Σ q XX as statistics of the first normal distribution corresponding to the qth phone, an average μ q Y and an auto-covariance Σ q YY of the second normal distribution corresponding to the qth phone, and feature information X of voice of the first speaker, the following Equation: μ q Y + ∑ q YY ∑ q XX - 1 ⁢ X - μ q X or the following Equation: μ q Y + ε ⁢ ∑ q YY ∑ q XX - 1 ⁢ X - μ q X wherein ε is an adjusting coefficient (0<ε<1).