A device and method for continuously producing an at least partly hollow shaft having a varying inner diameter includes forging tools that are arranged centrally symmetrically about a forging axis and are driven radially, a clamping chuck for holding an at least partly hollow cylindrical blank, and a counter-holder for axially supporting the blank. The counter-holder has a base and a counter-holder mandrel arranged on the base and extending axially into a central cavity in the blank. The mandrel is formed of at least two parts, wherein a first part of the counter-holder mandrel constitutes an inner part and a second part of the counter-holder mandrel constitutes an outer part surrounding the inner part. At least the outer part can be moved axially relative to the inner part.