PURPOSE: To make control of the varied quantity of temp. sensibility easy and to stabilize aging characteristics of the titled sensor by constituting it by doping other rare earth metallic ions excluding elements constituting a base body to the base body consisting of at least one element among La, Yb and Gd.

CONSTITUTION: At least one element among yttrium, lanthanum, ytterbium and gadolinium is used as the component of the light-transmittable base body constituting the temp. sensor in which at least one optical absorption band is caused and whose light transmissivity near the absorption band is varied with temp. The doped impurity is selected from other rare earth metallic ions excluding the elements constituting the base body.