Machining unit and machine tool

A machine tool that machines a workpiece by causing a tool to be revolved with a main spindle section being driven and rotated, comprising:

• a mechanism to move the main spindle section straight along an axial direction of a rotation center of the main spindle section;
• an eccentric rotational section that is disposed on the main spindle section and is rotatable about an eccentric axis, the eccentric axis being located eccentrically at any distance in a radial direction of the main spindle section from the rotation center of the main spindle section;
• a tool holder that is disposed on the eccentric rotational section and that holds the tool;
• a tool revolution-radius changing mechanism that moves the tool in the radial direction of the main, spindle section and changes the radius of revolution of the tool by rotating the eccentric rotational section about the eccentric axis;
• and
• a cutting-edge-orientation correcting mechanism that corrects the orientation of a cutting edge of the tool by making the tool holder spin about an axis of the tool holder, the axis being parallel to the rotation center of the main spindle section, wherein
• the main spindle section has a cam groove formed thereon,
• the tool holder is provided with an arm having a cam follower,
• the cam groove is engaged with the cam follower, and
• the orientation of the cutting edge of the tool is corrected by rotating the eccentric rotational section about the eccentric axis so as to cause the cam follower to move while being restricted by the cam groove and to cause the tool holder to spin about the axis parallel to the rotation center of the main spindle section via the arm.