A radiation clinical thermometer for making no-contact measurements of the temperature of the eardrum, comprising a light receiving section (17) for receiving only infrared rays radiated directly from the eardrum and/or its vicinity, a signal processing means (4) for calculating the temperature from the output of the light receiving section, and an annunciation means (18) for annunciating the calculated temperature. Because the thermometer is not influenced by the heat radiation from other than the eardrum and/or its vicinity, the temperature variation of the probe (1) does not cause measurement errors and therefore an accurate temperature measurement can be made. When viewed at the cross section of the thermometer including the optical axis of the light collecting element, the infrared light receiving element is placed in a triangle formed by three lines connecting three points, and an intersection between the optical axis of the light collecting element and an optical path where a line drawn from the edge of the light collecting element in such a way as to be tangent to the inner wall of the probe on the same side as the edge of the light collecting element with respect to the optical axis extends from an imaginary end where the line intersects the end surface of the probe and passes through the edge of the light collecting element on the same side as the imaginary end point with respect to the optical axis to reach an image point of the imaginary end point by the light collecting element. The remaining two points are two image points of the light collecting element at the imaginary end point.