PURPOSE: To contrive efficient dehydrating treatment of dredged sludge by primarily sieving earth, sand and mud of water bottom supplied with a dredge bucket, etc., to select them and furthermore secondarily selecting them while using a mesh wire gauze as a sieve.

CONSTITUTION: At least two pieces of shafts 5 are rotatably supported to the bottom part of a hopper 2 respectively and a plurality of scraping blades 6 which are mutually interposed between the other blades are fixed to the shafts 5 in the lengthwise directions at constant intervals. Further a casing 3 is provided to the lower part of the hopper 2 so that the scraping blades 6 can be rotated and the lower part of this casing 3 is opened and a pair of backup plates 10 are tiltably provided to the lower parts thereof. Vibrators 16 are fixed to the backup plates 10 respectively and also mesh wire gauzes 15 are provided to the side end parts. As a result, dredged sludge can be separated into high-liquid substance and high-solid substance and carried out before treating it with a dehydrator and therefore efficiency of dehydrating operation for dredge sludge can be remarkably improved.