PURPOSE: To realize high accuracy in a small type by setting a dimension of a light receiving part of an infrared ray sensor of a radiative clinical thermometer to measure an eardrum temperature and a diameter of an optical lens not more than a specific value.

CONSTITUTION: An infrared ray emitted from an eardrum 7 is condensed through an optical lens 3, and enters an infrared ray sensor 1 from an opening part 8, and forms an image in a sensor light receiving part 2. An angle of visibility is determined by the size of the sensor light receiving part and a distance between this light receiving part and the optical lens, and since the size of a visual field on a measuring object is determined by this angle of visibility and a distance between the measuring object and the optical lens, a sufficiently small visual field and sufficient optical sensitivity are obtained to the eardrum by a combination of the infrared ray sensor on which a light receiving diameter or one side of a square is not more than 0.3mm and the optical lens whose diameter is not more than 6mm, and influence of disturbance is hardly exerted. Therefore, a smaller angle of visibility is obtained, and a visual field is limited within a range of the eardrum, and measuring accuracy can be improved by eliminating temperature information except the eardrum.