The thermal conductivity of silicate melts at high temperatures was determined by applying a differential three-layered laser flash method. In this method, the correction for radiative heat transfer was indispensable to obtain accurate thermal conductivity of the melts at high temperatures because, at 1 500 K, the uncorrected values are 20 to 40% larger than the corrected ones; further, the corrected values strongly depend on the absorption coefficient of silicate melts. Recently, we applied the front-heating front-detection laser flash method using a short initial time period immediately after laser pulse irradiation for silicate melts. This method was considered to be unaffected by the radiative heat transfer. However, the amount of the radiative effect on thermal conductivity was not estimated. On the basis of heat transfer theory, the temperature responses of this method were numerically calculated by considering radiative heat transfer. The result revealed that the radiative effect is less than 4.4% even at 1 743 K.