To develop the method to analyze transient characteristics of the combined radiative and conductive heat transfer in the industrial furnaces, heat transfer in vacuum furnaces is numerically analyzed. The vacuum furnace is heated by several radiant tube burners and enclosed with thermal insulation walls. Object materials to be heated are placed at the central region of the furnace. A three-dimensional computer program for general purpose is developed to solve radiative heat transfer within enclosure including the transient conductive heat transfer within the insulation walls surrounding the system. The Monte Carlo method is used for the radiative heat exchange calculation. The results of the numerical simulation are compared with the results of experiment. The simulated results fit very well with the experimental ones, which shows the validity of the present simulation method.