An illuminating device includes a discharge lamp, a condenser lens, an integrator lens, a polarization conversion system, an electromagnetic wave shielding plate, and an electromagnetic wave shielding wall. A light given out from each lens in the light-incident-side fly's eye lens becomes two light fluxes via respective polarizing beam splitters and the two light fluxes pass through two lenses in the light-exit-side fly's eye lens. The electromagnetic shielding plate has an aperture on an optical axis of each lens in the light-exit-side fly's eye lens. The electromagnetic wave shielding plate is grounded through the electromagnetic wave shielding wall.