Abstract: A chalk-dust collecting apparatus for blackboard erasers has a housing that contains a dust-collecting bag, a filter and a vacuum suction device. The housing is affixed with an upper lid on the top thereof. The dust-collecting bag is with its top end attached by a lid. The lid is received by the outer shoulder portion of the intermediate cover and comprises a plurality of lower air inlet slits. Further, the upper lid has a plurality of upper air inlet slits arranged correspondingly to the lower air inlet slits in the manner that each said upper air inlet slit is intercommunicated with a respective said lower air inlet slit. Thereby, chalk dust at the upper air inlet slits can be directly sucked into the bag through the lower air inlet slits and prevented from diffusing between the dust-collecting bag and upper lid. Thereby cleanness of the apparatus can be achieved.