This is a device for cleaning a blanket mounted around a cylindrical drum of a printing machine. The device has a vessel arranged to open upward with an upper opening thereof facing a downwardly convexed bottom portion of the blanket and supported to be movable up and down, a pair of rollers mounted in the vessel adjacent the opening thereof so as to carry a strip sheet material thereon as bridging therebetween, and a nozzle mounted in the vessel so as to project a jet flow of a cleaning fluid upward against the bridging portion of the strip sheet material. In cleaning operation, the bridging portion of the strip sheet material is pressed against the downwardly convexed bottom portion of the blanket by the pair of rollers with the vessel moved upward, and the blanket and/or the strip sheet material is moved relative to one another so that the blanket is given a rub cleaning action by the strip sheet material under supply of an effluent amount of the cleaning fluid which also agitates a layer of the cleaning fluid suspended in contact with the blanket by a substantial kinetic energy supplied with the jet flow.