1. A fingerprint ridge image synthesis system, comprising an image synthesis main unit which extracts ridge shapes contained in a fingerprint image and synthesizes a ridge image of the fingerprint image based thereupon, wherein the image synthesis main unit comprises: a wavelet setting unit which sets different wavelet wavelength (λ) and wavelet angle (θ) as parameter values of wavelets and also sets combinations thereof as parameter sets by corresponding to gradient of each pixel of the fingerprint image; a ridge pixel parameter calculation unit which includes a continuous wavelet transforming function for performing continuous wavelet transform processing on partial regions within the fingerprint image corresponding to each of the pixels based on each of the different parameter sets, calculates consistency between the wavelets corresponding to each of the parameter sets and ridge shapes in each of the partial regions, and determines the parameter set of the highest consistency as the parameter set corresponding to each of the pixels; a label optimization processing unit which updates/converts the parameter values of the parameter sets of each of the pixels and each of neighboring pixels neighboring to those pixels to optimal values with which mutual continuity of the parameter values becomes optimum; and a ridge image generation unit which synthesizes the ridge image by setting gray-scale values of each corresponding pixel based on the parameter sets constituted with the optimal values.