PURPOSE: To suppress the scattering of a chalk powder to the circumference and to enhance the wiping workability of a blackboard by fitting an air suction port to the periphery of the surface of the blackboard and connecting the air suction port and a dust collector by a duct.

CONSTITUTION: When the character written on the surface 5 of a blackboard is erased by an eraser, a chalk powder flies up but the chalk flewn up in the vicinity of the surface 5 of the blackboard is sucked from the air suction port 6 to pass through a duct 8 and a gathering pipe 9 to be stored in a dust collector 10. A metal net 7 prevents the invation of foreign matter into the air suction port 6.