PURPOSE: To make miniaturization and lightweightiness come to fruition, by constituting mud conveying part with a belt conveyor and a cover member being set up adjacently at the upper side, while forming a sand and earth conveying space capable of conveying these sand and earth as held between both.

CONSTITUTION: A belt conveyor support ladder 21 is rockably supported on the hull 20 of a dredger via a ladder wire 27, and a bucket wheel 24 as a dredging part is set up at the tip end part. A belt conveyor 7 constituting a mud conveying part and a cover member 12 to be installed as adjoining with the upper side both are set up inside the ladder 27. The belt conveyor 7 is turned round in an (a) direction by a drive pulley 4. And, an upper belt 3 of the belt conveyor 7 is bent by dint of carrier rollers 5aW5c, and both these side end parts is made contact with the cover member 2 whereby a sand and earth conveying space 8 is made formable mutually between the cover member 2 and the upper belt 3.