To provide a machine tool, surely supporting a tool to be held on both sides without any influence of a change in work diameter and abrasion of a tool.

A tool support unit 20 is composed of a movable part 21 having a support member 22 for rotatably supporting the other end of a hob H, one end of which is mounted on the spindle head 9, through an arbor A and a fixed part 35 fixedly set on a turret 14 to slidably support the movable part 21. The movable part 21 includes: a first holding member 24 rotatably holding the support member 22; second holding members 25a, 25b holding the first holding member 24 to rotate around the axis orthogonal to the rotating shaft of the support member 22; and a slide member 27 fitted to a slide guide connected to the second holding members 25a, 25b and formed on the fixed part 35. When the tool support unit 20 is indexed to a tool support position, the movable part 21 is moved forward and backward in the Y-axis direction.