PURPOSE: To uniformly ignite the whole surface area of granular combustible material, by producing explosive combustion by introducing fresh air after filling the upper space of a sintering truck with volatile gas.

CONSTITUTION: When the damper 9 of a wind box 9 is opened with an ignition cover 8 being covered, open air is introduced from the gap between the ignition cover 8 and a sintering truck 5, at the same time the air in the sintering truck 5 is sucked downwardly. Then voltile gas filling the upper space 10 of a sintering truck 5 is burned explosively in a moment. Since combustion occurs in the whole inside part of an upper space 10, the whole surface area of granular combustible material loaded on the sintering truck 5 can uniformly be ignited. By this method, the combustion temperature and the combustion time for the granular combustible material can be kept uniformly, so that uniform and lightweight frame material can be obtained.