This invention relates to an optical fiber and others having a structure for efficiently generating SC light while realizing high nonlinearity over a wide band. The optical fiber has at least a center core region, and an outside cladding region having a refractive index lower than that of the center core region and provided on an outer periphery of the center core region. The optical fiber has, as characteristics to light of a wavelength λ1 in a wavelength range of 1520 nm to 1620 nm, a chromatic dispersion of −2 ps/nm/km to +2 ps/nm/km, a dispersion slope of −0.009 ps/nm2/km to +0.009 ps/nm2/km, and a fourth-order dispersion of −1.8×10−4 ps/nm3/km to +1.8×10−4 ps/nm3/km.