In a reflecting type overhead projector, a reflecting table is formed of a Fresnel lens and a mirror laid together with the mirror lying close under the lens, and the original is laid against and above the lens. A lamp above the reflecting table projects light towards the original. A projection lens above the reflecting table projects an image of the original upon the screen. A photosensitive element near the reflecting table responds to the light from the lamp. A control circuit receives a signal from the photosensitive element and controls the intensity of the light emitted by the lamp. The control circuit supplies full power to the lamp, lighting it more brightly, when first the lamp is to be turned on. Thereafter, when the lamp is being supplied with full power so as to light it more brightly, and then the intensity of light radiation received by the photosensitive element drops substantially, the control circuit supplies part power to the lamp so as to light it less brightly; and, when the lamp is being supplied with part power so as to light it less brightly, and then the intensity of light radiation received by the photosensitive element rises substantially, the control circuit supplies full power to the lamp so as to light it more brightly. Thus when the operator's hand is put under the lamp the lamp is dimmed; and thus the danger of the operator being burnt by the light from the lamp is avoided.