PURPOSE: To obtain the title apparatus capable of accurately measuring the expansion coefficient of a sample without applying load to the sample at the time of measurement.

CONSTITUTION: A sample 203 is heated by a heater 104 or cooled by a cooler 110 so as to be adjusted to the temp. value set by an operation panel 108 setting a temp. value for measuring the expansion coefficient/shrinkage factor of the sample 203. One end of the sample 203 is fixed and the leading end of the other end of the heated or cooled sample and the vicinity thereof are irradiated with the light from a light emitting part 102 and the change quantity of the length of the sample 203 is detected on the basis of the quantity of transmitted light. From the set temp. value and the detected change quantity of the length of the sample, the expansion coefficient/shrinkage factor of the sample is calculated.