To improve energy-saving by shortening a drying time by preventing inhibition of heat transfer by accumulation layer of a treated object attaching and growing on a tank inner wall of a drying machine in drying food residue.

A scraper made of an elastic abrasion-resisting material is held without using a bolt, constantly kept into contact with the tank body inner wall by utilizing a corner of the scraper, and reversed up side down to be reused when the corner is abraded. Further heat transferring can be improved as the scraper follows thermal expansion of a wall surface and reduces and removes an accumulated deposit on the wall surface.