1. A wavelength conversion optical device including: a fundamental wave light source for outputting a fundamental wave light; and a wavelength conversion mechanism including a polarization inversion unit for wavelength-converting the fundamental wave light emitted from the fundamental wave light source to generate harmonic waves; wherein said fundamental wave light source is a fiber laser light source which outputs a fundamental wave light having polarized light components in two directions perpendicular to each other, said polarized light components having different wavelengths; and said wavelength conversion mechanism wavelength-converts the fundamental wave light for each of the polarized light components in the two directions perpendicular to each other.