Abstract: An ultraviolet irradiation device of the optical path division type for treating a workpiece which is often subject to deformations and color changes due to heat, and in which the distribution of radiance is good and the average irradiance on the surface irradiated with light can be increased which can be achieved with light emitted from a rod-shaped lamp and reflected by a trough=shaped cold mirror being incident in cold mirrors which split the optical path. This light is thus divided into two parts and is incident in total reflection mirrors. On the other hand, the direct light emitted by the rod-shaped lamp is incident in second optical path splitting cold mirrors which divides this light and causes it to be incident in the total reflection mirrors. The light reflected by the total reflection mirrors is incident in heat reflection filters, and is transmitted by the heat reflection filters so as to be radiated onto a workpiece.