PURPOSE: To allow smooth passage of foreign matter, etc. between an upper roller and a lower roller without clogging even if such matter, etc. are supplied to a dehydrator by providing scrapers on at least one roller side of the upper and lower rollers so that the material to be dehydrated is forcibly conveyed to between both rollers.

CONSTITUTION: A material M to be dehydrated is supplied to a casing 23 and is moved up to the position where a rotating upper roller 2 and a lower roller 4 face each other. The two scrapers 7, 8 provided on the roller 2 side are guided by rollers 13, 15 rolled in a guiding groove 21. Foreign matter and solid matter are therefore forcibly transferred between both rollers 2 and 4 by the scrapers 7, 9 even if such foreign matter and solid matter exist in the material M.