To provide a cleaning method for an existing pipeline capable of cleaning the pipeline having the diameter larger than that of a drain branch pipe by utilizing a facility giving the blast quantity required for the drain branch pipe.

In this cleaning method for the existing pipeline 1 removing the stacked objects on the inner face of the pipeline 1 with the abrasives air- conveyed in the existing pipeline 1, a sucking device 3 is connected to one end in the installation direction of the existing pipeline 1, and a storage section 4 of the abrasives S communicated with the existing pipeline 1 is arranged at the other end in the installation direction of the existing pipeline 1. The abrasives S are sucked and conveyed in the existing pipeline 1 from the storage section 4 via a feed hose 5 inserted into the existing pipeline 1, and the suction air quantity in the existing pipeline 1 and the suction air quantity in the feed hose are adjusted on the other end side in the installation direction of the existing pipeline 1 and in the feed hose 5.