PURPOSE:To wash and clean up carbon in an air-tight chamber by a method in which an air-tight chamber is provided in such a way as to cover the air entrance port of a hammer, and compressed air mixed with a cleaner to clean up carbon is sent into the air-tight chamber. CONSTITUTION:When a hammer 3 is lifted up and dropped, oil on the head 2 of a pile 4 is ignited and exploded by the hammer 3, while a compressed air mixed with a cleaner to clean up carbon adhered which is hard to ignite is supplied into the air-tight chamber 7 through an air supply port 9 and a check valve 8. During the explosion period, the supply of the compressed air is temporarily stopped. The explosion exhaust gas from the air entrance port 5 is discharged from the air-tight chamber 7 through a check valve 10 and an exhaust port 11 by high-pressure air which again starts flowing. The explosion exhaust gas does not flow back by the check valve 9 and air is not sucked by the check valve 10. The exhaust gas is completely burned in the air-tight chamber 7 by the compressed air, and carbon in the air-tight chamber 7 is washed and cleaned by the cleaner.