An assembly device for assembling and disassembling a rotor of a turbomachine with rotor disks that are clamped together by at least one tie rod is provided. The assembly device includes a turning block that is secured to a base and a securing device that secures the rotor against tilting. The rotor is arranged in a transversal manner in relation to a horizontal plane of the base and pivotably mounted on the turning block. The securing device is fixed to the base by several supports and the turning block is arranged inside the surface of the base that is clamped by the supports. Large forces and torque coming from the rotor that is arranged in a perpendicular manner are guided from the securing device to the base.