Abstract: An electronic clinical thermometer includes a liquid crystal display element for displaying the result of a temperature measurement, and a lamp circuit for illuminating the liquid crystal display element automatically at the end of the temperature measurement only when a sensed amount of ambient light is insufficient to permit easy reading of the temperature displayed by the liquid crystal element. The lamp circuit is switched on and off electronically, eliminating the need for mechanical contacts and manually operated push-buttons, thus making it possible to obtain a liquid-tight structure.