An ultraviolet light source (1) comprises a laser light source (10) for generating a signal light in the infrared region, a optical amplifier (20) which comprises fiber optical amplifiers (21, 22) and amplifies the signal light generated by the laser light source (10), and a wavelength converting optical system (30) which coverts the signal light amplified by the light amplifier (20) into an ultraviolet light and outputs the converted light. The ultraviolet light source (1) uses a single-mode fiber laser (26) as an excitation light source for at least the fiber optical amplifier (22) at one stage of the optical amplifier (20).