A light source apparatus is used in a video endoscope system having a charge coupled device (CCD) image sensor and a monitor. The light source apparatus provides illumination to a scene to be imaged by the CCD image sensor and displayed on the monitor. The light source apparatus includes a discharge lamp serving as a light source. The lamp is subject to progressive degradation during use so that its output light intensity achievable with a given level of input current gradually decreases through its lifetime. The current supplied to the lamp is controlled using a feedback control technique so as to maintain the output light intensity of the lamp at a substantially fixed, desired intensity level. In order to allow the operator to timely replace the discharge lamp with a new one, the input current to the discharge lamp is detected and compared to a threshold level. The threshold level may be selected to a level corresponding to the rated power of the lamp designated by the manufacturer. The input current has a tendency that its level for achieving a given level of output light intensity of the lamp gradually increases through the lifetime of the lamp, which is caused by progressive degradation of the lamp while the output light intensity level is controlled to be at a substantially fixed level. When the level of the input voltage has reached the threshold level, a visual alarm indication is provided on the monitor, indicating the necessity for replacement of the discharge lamp.