1. A speech synthesis method comprising: an acquisition step of acquiring micro-segments from speech waveform data and a window function; a correction step of correcting the micro-segments using a spectrum correction filter formed based on the speech waveform data to be processed in the acquisition step, wherein the spectrum correction filter emphasizes the formant of the micro-segments, wherein the spectrum correction comprises a FIR filter whereof the coefficients are acquired by truncating impulse response of a filter having a characteristic represented as F 1 ⁡ ( z ) = ( 1 - μ ⁢ ⁢ z - 1 ) ⁢ 1 + ∑ j = 1 p ⁢ α j ⁡ ( z / γ 1 ) - j 1 + ∑ j = 1 p ⁢ α j ⁡ ( z / γ 2 ) - j wherein α j is a coefficient acquired by p-th order linear predictive analysis on the speech waveform and μ, γ 1 , and γ 2 are appropriately defined coefficients; a re-arrangement step of re-arranging the micro-segments corrected in the correction step to change prosody upon synthesis by repeating a given micro-segment corrected in the correction step; and a synthesis step of outputting synthetic speech waveform data on the basis of superposed waveform data obtained by superposing the micro-segments re-arranged in the re-arrangement step.