PURPOSE: To detect surely conditions of a filter, by providing a means, which measures the quantity of toner supply, in a developing part and detecting clogging conditions of the filter on a basis of the measured result.

CONSTITUTION: When a heater 9 fixes a toner, which is transferred to a recording paper 7, by heating, soot and smoke generated from the toner are discharged from a fixer 8 by a blower. Soot and smoke are eliminated by a filter 10 provided in the exit side of the air passage. The quantity of atrraction of soot and smoke of the filter 10 is increased according as the operation time of a printer elapses, and clogging occurs, and the function is degraded gradually. During this time, a counter 11 counts the number of times toner supply of a supply equipment 2; and when the counted value reaches a preliminarily set value, the time of replacement of the filter 10 is reported by an alarm 12.