An anode electrode (10) is composed of a long straight cylinder-shaped body, and the outer circumference of the cylinder-shaped body is covered with a dielectric (12). A cathode part (20) has a shape of straight half cylinder. A cathode (25) surrounds the anode, and the anode and the cathode are arranged parallel to one another in the lengthwise direction. The cathode is provided with a cathode wire group (16). In the cathode wire group, both edges of the wire are fixed at both edges (20D) of the half cylinder shaped body constituting the cathode part, in the lengthwise direction, so as to have the plurality of wires parallel to one another. On a surface (20S) of the cathode part on a side that faces the anode, a reflecting plane is formed for reflecting radiation in a vacuum ultraviolet region. Thus, high-intensity light having a wavelength in the vacuum ultraviolet region can be obtained, and an object to be irradiated can be efficiently irradiated with the light.