Abstract: There is provided a radiation clinical thermometer which does not require experience and can measure an accurate body temperature easily and quickly since the user recognizes that a probe is correctly directed toward an eardrum. When a measured temperature is in a predetermined range, it is determined that the probe is inserted in an ear, and a level 1 is displayed. When a first maximum value of temperature measurement values appears, a level 2 is displayed. When a second maximum value of temperature measurement values appears, a level 3 is displayed to notify the user of the optimum insertion state for body temperature measurement.