A pitch-estimation method, a pitch-estimation system, and a pitch-estimation program are provided, which estimate a weight of a probability density function of a fundamental frequency and relative amplitude of a harmonic component through fewer computations than ever. In the improved pitch-estimation method, 1200 log2 h and exp[−(x−(F+1200 log2 h))2/2W2] in the following expression are computed in advance and then stored in a memory of a computer: c ′ ⁡ ( t ) ⁡ ( h ❘ F , m ) ⁢ 1 2 ⁢ π ⁢ ⁢ W 2 ⁢ exp ( - ( x - ( F + 1200 ⁢ ⁢ log 2 ⁢ h ) ) 2 2 ⁢ W 2 ) ( 61 ) The above expression is computed only with respect to a fundamental frequency F wherein x−(F+1200 log2 h) is close to zero. With this arrangement, computations to be performed may considerably be reduced, and computing time may accordingly be shortened.