A fiber optic device outputs, at high conversion efficiency, an idler lightwave having a wavelength λ2 different from the wavelength of a signal lightwave by converting the signal lightwave having an optional wavelength λ1 in a wide wavelength band. The fiber optic device comprises a wavelength tunable pump light source for outputting a pump lightwave having a wavelength of 2×(λ1−1+λ2−1)−1; a optical coupler for coupling and outputting the pump lightwave and the signal lightwave; and an optical fiber having a length of 450 m or less, the zero-dispersion wavelength thereof being in the wide wavelength band, the dispersion slope thereof at the zero-dispersion wavelength being +0.01 ps/nm2/km or more and +0.045 ps/nm2/km or less, wherein the optical fiber allows propagation of the signal lightwave and the pump lightwave output from the optical coupler, and generates an idler lightwave by means of the nonlinear optical phenomenon that occurs during such propagation.