A shaft-type furnace model, in which the furnace Column was divided into multi cells, was designed and incorporated with equilibrium reaction calculation software for studying the volatilization behaviors of low-boiling-point metals of Pb and Na, K during gasification and melting process of municipal solid wastes in a shaft type furnace. The volatilization behaviors of Na, K and Pb were discussed by comparing the results on volatilization of Na, K and Pb derived by the equilibrium calculation with the data obtained from an actual operation unit. As a result, it was found that Na, K and Pb were volatilized mainly as chloride forms in the temperature range up to approximately 1173 K and were volatilized as metallic forms with a further rise in temperature. It was also found that the chloride volatilization ratio of Pb increased with an increase in chloride content, and that the volatilization of metallic Pb became dominant when the oxygen partial pressure was below 1 x 10(-7) MPa. From the results of a pilot-plant and a laboratory-scale melting tests, it was recognized that Pb concentration in slag decreased as the oxygen partial pressure decreased, and that the remaining Pb ratio in slag decreased as the basicity of slag increased. These results on volatilization behavior of Pb were well represented by the equilibrium calculations using the proposed shaft type furnace model.