PURPOSE: To take advantage of the merits of the calibrating method and to perform superior measurement by bringing a plate type heater into contact with a sample, measuring a temperature rise and fixing the heat conductivity of the sample according to a data which is calibrated with a sample whose conductivity is already known.

CONSTITUTION: One surface of the thin plate type heater 1 is insulated by a heat insulating material 4 and the other surface is brought into thermal contact with a semi-infinite body sample 2 to heat it stepwise. Then the rising temperature of the heater 1 at proper time after the start of the heating is measured by a thermocouple 3 and the heat conductivity of the sample is found according to the relation between the rising temperature and heat conductivity of the heater calibrated with the sample whose heat conductivity is already known. Thus, the thin plate type heater 1 is used, so the rising temperature of the heater can be handled like a spot heat source and the calibration section for the heat conductivity is divided into several small sections to eliminate the influence of the heat capacity, thereby performing superior measurement by taking advantage of the merits of the calibrating method.