A thermal conductivity estimation method includes: measuring temperature distribution of a measurement sample surface in a steady state by partially heating the measurement sample under predetermined heating conditions; calculating temperature distribution of a sample model surface by performing a heat-transfer simulation on the sample model of the same shape as the measurement sample for a plurality of combinations of provisional thermal conductivities and heating conditions; making a regression model, whose input is temperature distribution of the measurement sample surface and whose output is a thermal conductivity of the measurement sample, by a machine learning technique using training data in a form of a calculation result of the plurality of combinations and the temperature distribution obtained from the plurality of combinations; and estimating the thermal conductivity of the measurement sample by inputting a measurement result of the temperature distribution of the measurement sample surface into the regression model.