To exercise the scraping function of a blade without affected by the sludge or the like, by not having the gaps between an inner face of a housing and an outer face of an elastic body, and between a peripheral face of a through hole and an outer face of a rod.

A scraper unit 13 comprises a square bar shaped first elastic body 53 which is fitted into a square tubular first housing 51 for the fore and aft movement, of which the both edge openings face in a lateral direction, and has a first through hole 52, of which a cross section has shape of a longitudinal rectangle, and is extended in the lateral direction, a tie plate-shaped first rod which is penetrated through the first through hole 52 in a condition that the left and right both edges are projected, and an almost vertical gate type plate-shaped scraping blade 56 of which the lower edge parts are mounted on the left and right both edges of the first rod, striding over the first housing 51, and which has a scraping blade 55 on an upper edge part. An inner face of the first housing 51 and an outer face of the first elastic body 53 are closely kept into contact with each other, and they are free from a gap. A peripheral face of the first through hole 52 and an outer face of the first rod 54 are closely kept into contact with each other, and they are free from a gap.