An apparatus for feeding bars (2) to a machine tool comprises an end (3) suitable for being placed in a position adjacent to a working zone(4) in which spindle means (5) of the machine tool are provided; a drum element (6), close to the end (3) and rotatable around a rotation axis (X); movable supporting means (7) provided on the drum element (6) for supporting and guiding a bar (2) parallel to the rotation axis (X). The movable supporting means (7) are slidably drivable on the drum element (6) parallel to the rotation axis (X) between a disengagement retracted configuration (R), in which the movable supporting means (7) are gathered nearer the working zone (4) to enable a respective bar (2) to be loaded, and an engagement extended configuration (E), in which the movable supporting means (7) are spaced away from the working zone (4) and are distributed along a supporting zone (S), opposite the working zone (4) with respect to the drum element (6), to engage the respective bar (2) to be supported and guided during machining. The movable supporting means (7) comprise telescopic tubular means (8) configured for being received, in said disengagement retracted configuration (R), inside tubular housing and guiding means (9) suitable for coupling with the spindle means (5). The telescopic tubular means (8) define, in the engagement extended configuration (E), a cylindrical containing structure configured for enclosing and supporting in a distributed manner a respective bar (2) along the entire supporting zone (S), so as to prevent the bar (2) from flexing because of the centrifugal actions generated by the rotation.