PURPOSE: To perform smooth firing and combustion, by coupling the delivery pipe of a blower for primary air to a heating pipe for preheating the air.

CONSTITUTION: A primary air, injected together with fuel through a burner 23 installed to the top end of a rotary kiln 11, is pressurized by a blower 27 for primary air, and a delivery pipe 28 thereof is coupled to heating pipe groups 25, 25'... for preheating the air installed in a manner to cover a refractry structure at a corner part 24 at the forward end of the ceiling of a clinker box 1. Thus, the high-pressure primary air flows to the burner 23 as it is heated during passage of it through the heating pipe groups 25, 25'... and pressure thereof is maintained, and the primary air is injected forcibly through the burner 23. In this case, temperature of the primary air fed to the burner is 800W500°C, pressure is 1,000W2,000mmH2O, and the amount of the primary air can be reduced to 2% of the total air amount.