PURPOSE: To provide a calibration device for accurately calibrating an optical thermometer.

CONSTITUTION: A calibration device for calibrating an optical thermometer which is optically connected via an optical fiber to a light reception rod having an incidence light port for beams to enter its tip is constituted of a cylinder 61 for inserting the light reception rod 10, an electrode switch 65 for recognizing that the light reception rod 10 has been inserted into the cylinder 61, an electric bulb 64 for calibration being provided at the closed part of the cylinder 61, a constant current source 8 for turning on the electric bulb 64 for calibration at a calibration temperature, and a controller 7 for operating the constant current source 8 according to the output of the electrode switch 65.