A tool-holder unit for processing a tube comprises at least two tool supports (10), each of which rotatably supports a tool shaft (12) on which a tool (14) for processing the tube is suitable for being mounted so that the tool (14) processes the side surface of the tube. The tool supports (10) are mounted on a support-holder body (16) having a toroidal shape. At least one of the tool supports (10) is supported by the support-holder body (16) by means of radial movement means, which are operable for moving the tool support so that the respective tool (14) translates radially with respect to the tube to be processed. A transmission system is suitable for transferring the rotation of the support-holder body (16), driven by a motor apparatus, to the tool shafts (12) so as to obtain a motorized rotation of the tools during the processing.