PURPOSE: To prevent the occurrence of noise by absorbing the vibration of the rocking shaft of a sprocket wheel for chain by a damper in a grit raker operating a bucket chain in a sedimentation basin.

CONSTITUTION: A bucket chain 6 is placed in a freely operable manner in a sedimentation basin, and the rocking shaft 3 of a sprocket wheel on the inflow side which is engaged with the chain 6 is rotatably supported by a support shaft 4 through an arm 5 and connected with a damper A. When the tension force F of the chain is abnormally and abruptly increased, the occurrence of vibration is suppressed and prevented by the damper A although the shaft 3 is apt to rise.