Abstract: The present invention relates to a reamer for hollow shafts of turbines. Particularly the invention relates to a reamer for hollow shafts, and comprises a casing provided with self-centering means for insertion into the shaft bore, a motor slidable axially inside said casing, means for moving said motor axially, a drive shaft rotated by said motor rigid therewith in its axial movements and keyed to a reaming head which is rotatable relative to said casing but axially fixed relative thereto; the invention further comprises at least one reaming tool rotated by said reamining head, and cam means for guiding said reaming tool along a curved trajector lying in a radial plane of said reaming head and operated by the axial movement of said drive shaft.