PURPOSE:To keep off localized overheating in a trap by installing a shielder in space between a trap inlet port and a heater, and moving the shielder so as to cause a temperature difference between a trap central part and the inner circumferential part to be within the specified value. CONSTITUTION:A heater 3 is installed at the upstream side of a particulate trap 2, while a muffler 8 is installed in the space between a trap inlet part 2a and this heater 3. Each of temperature sensors 7 and 4 is installed in a central part and an inner circumferential part of the trap 2, and each censor output is inputted into a controller 7. And, when the heater 3 is energized with current and the trap 2 is subjected to afterburning, a motor 9 is driven so as to cause a difference in each detected temperature of both these sensors 4 and 7 to be within the specified value, thereby controlling the position of a shielder 8. With this constitution, overheating in the central part of the trap is preventable.
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