An electronic thermometer including a probe to be inserted in to a portion of an outer ear to be measured by the thermometer, an infrared quantity detection means for detecting an infrared radiation quantity which is entered through the probe, a temperature computation means for applying the detected infrared radiation quantity in a predetermined computation expression to compute out a temperature such as body temperature, an infrared transmission data reading means for taking data corresponding to an infrared transmission quantity passing through the probe, and a control means for controlling the computation expression according to the taken data corresponding to the infrared transmission quantity.