A printing cylinder assembly for a printing machine having a sleeve cylinder which can be simply coupled to and decoupled from a rotating shaft and which can be exchanged easily. The sleeve cylinder is mounted to fit on the rotating shaft so that it can be fitted on, and be extracted from, the rotating shaft, constituting a printing cylinder. The rotating shaft is provided with a cam shaft and a coupling member that constitutes a coupling mechanism. In a coupling and a decoupling state which the coupling mechanism comes into, rotations of the cam shaft cause the coupling member to couple and decouple the sleeve cylinder to and from the rotating shaft when the coupling member is diametrically urged against, and parted from, the inner diametric surface of the sleeve cylinder, respectively.