A bulk crystal type optical wavelength converter device (110) is made of a monocrystalline nonlinear optical material (3,5-dimethyl-1-(4-nitrophenyl)pyrazole, referred to as PRA). A linearly polarized fundamental having a wavelength ranging from 900 to 4000 nm is applied to the bulk monocrystalline nonlinear optical material to achieve angular phase matching of the type I for obtaining a second harmonic of the fundamental. An optical wavelength converter module comprises a fiber type optical wavelength converter device (110) and a light source device (120). The optical wavelength converter device (110) includes a core (111) made of a monocrystal of the PRA which has has a crystal orientation such that the c-axis thereof extends substantially along the axis of the core (111). The light source device (120) applies, to the optical wavelength converter device (110), a fundamental which is linearly polarized in the direction of the a-axis or b-axis of the crystal which is normal to the c-axis.