To estimate the progressing condition of sintering reaction in a Dwight Lloyd type sintering machine in high accuracy.

The temp. flow rate and components in the exhaust gas in plural wind boxes 7, 7,... in the Dwight Lloyd type sintering machine, are measured, and positions and shapes of a coke ignition line and a solidification completing line are estimated from the obtd. measured values. Since the position and the shape of the coke ignition line regardless of the coke distribution in the inner part of the raw material layer can be estimated, the progressing condition of the sintering reaction of the raw material layer can be estimated in the high accuracy.