An endoscope system is provided with a lamp for illuminating a body cavity through an endoscope, and a lamp energizing circuit for adjusting current to be supplied to the lamp. Control data for controlling the lamp is stored in a ROM. While the ROM is held in an enabling state by a chip selector according to setting data from switches and a zerocross detector, the control data is read out from the ROM by a CPU, and the lamp is energized in accordance with the control data. If the ROM is not in the enabling state although the CPU is fetching the setting data and control data, then an alarm signal is delivered from a NOR gate, and the lamp is so energized as to provide a maximum brightness.