Abstract: Disclosed is an electronic clinical thermometer at least the temperature sensing portion of which, or the entire thermometer, has a flexible structure which adapts itself to any part of a body surface for automatically measuring body temperature or body surface temperature over an extended period of time. Preferably, the thermometer includes a power supply battery and a temperature measuring and storing circuit for storing in memory temperature data obtained by sensing temperature at a predetermined period by means of a temperature-responsive portion, reading out the temperature data stored in the memory in response to an externally applied data-read request, and outputting the temperature data to an external unit from a prescribed signal extracting portion. These elements are mounted on a flexible circuit board.