PURPOSE: To prevent the decrease of dust collection efficiency, as well as to prevent black smoke, by directly feeding exhaust gas in high temperature into an electric dust collector when a combustion furnace is started, in an electric dust collector into which exhaust gas is fed from a combustion furnace for coal, through an economizer and the others.

CONSTITUTION: The exhaust gas in a combustion furnace 1 is deflated out of the furnace through a free part 2 and an economizer 3, and is discharged from a stack 6 into the open air, after coarse dust is removed from the gas by a multi- cyclone 4 and smaller dust is collected by a dry electric dust collector 5. In this apparatus, a bypass line 8 is provided to connect the upper part of an economizer 3, which is interconnected to the free part 2, with the upstream side of a dust collector 5, and a valve 7 is interposed in said line 8. The valve 7 is opened at the time when the gas temperature in the combustion furnace 1 is raised above 360°C, for instance, so that a part of exhaust gas in high temperature is fed into the dust collector 5 through the free part 2. Dust in exhaust gas can be collected in such a manner during the combustion furnace 1 is at work.