PURPOSE: To enable to effectively heat-exchange by a structure wherein a threaded fixed shaft is arranged between both cover plates and a nut fixed with a disc slidingly contacting onto the inner wall of a cylinder is screwed onto said shaft and turned together with the disc by means of a rotary plate with driving bars in the heat-exchanging device for high viscous waste oil or the like.

CONSTITUTION: The fixed shaft 5, one end of which is squarely protruded so as to fittingly fixed to the side cover 3 and the other end of which is journaled in the circular recess of a rotary disc 8 piercing a side cover 4 and further the intermediate part of which is provided with screw threads whereinto the nut 6 fixed with the rotary disc 7 slidingly contacting onto the inner wall of the cylinder, is provided at the center of the heat-exchanging device main body 1. The rotary disc 7 is moved back and forth while rotating by means of the rotation of a rotary shaft 10 through four rotary driving bars 9, which pierce the rotary disc 7 and at the same time are held between both the rotary discs 8, so as to scratch off sludge-like substance and the like fixed on the inner wall of the cylinder by separating due to the heating with heating fluid in a jacket 2. The scratched-off substance is scraped away with a scraping bar 17 into a receiver 18. Consequently, the heating surface is kept in a normal state, resulting in accomplishing effective heat exchange.