An illuminating device includes at least first and second nitride-based semiconductor light-emitting elements each having a semiconductor chip with an active layer region. The active layer region is at an angle of 1° or more with an m plane, and an angle formed by a normal line of a principal surface in the active layer region and a normal line of the m plane is 1° or more and 5° or less. The first and second nitride-based semiconductor light-emitting elements have thicnknesses of d1 and d2, respectively, and emit the polarized light having wavelengths λ1 and λ2, respectively, where the inequarities of λ1