To obtain a clinical thermometer wherein substantial infrared rays from an external acoustic meatus is an object for measurement by providing a light guiding part toward obliquely forward at an obliquely front of an infrared rays sensor and detecting the infrared rays incident from the light guiding part and converting it to a body temp. value.

A light guiding part 5b of the apex side part of a probe part 5 is formed by making a hole into the probe part 5 or is formed by forming another member as a plug body at the apex part of the probe part 5 and an infrared rays sensor 10 is provided on the same axial line as that of the probe 5 to the forward and the light guiding part 5b is arranged at the obliquely front of the infrared rays sensor 10 and the apex part 5a of the probe is arranged toward the obliquely forward by making a hole in the apex part 5a of the probe. When the probe 5 is inserted into the external acoustic meatus, the infrared rays sensor 10 is faced to the obliquely front external acoustic meatus and the incident infrared rays from the front being on the same axial line as the infrared rays sensor 10 is prevented from occurring by the apex part 5a on the same axial line as that of the infrared rays sensor 10. It is possible thereby to efficiently detect the infrared rays from te external acoustic meatus by the infrared rays sensor.