Tool radius adjusting method in machine tool and machine tool for practicing the method

A machine tool comprising:

• a boring holder provided with a housing and a movable body supported on the housing to be slidable relative to the housing in a direction to cross a rotational axis direction and having a reference portion;
• a cutting blade attached to the movable body;
• a tool spindle rotatably supported on a spindle head and holding the housing;
• a position adjusting reference member provided to be changeable in relative position to the tool spindle and provided to be contactable with the reference portion of the movable body;
• at least one drive mechanism being able to change the relative position between the tool spindle and the position adjusting reference member and used for positioning the spindle head relative to a workpiece in machining the workpiece with the cutting blade;
• and
• a control device for controlling the at least one drive mechanism to control the relative position between the tool spindle and the position adjusting reference member;
• wherein in the state that the position of the cutting blade comes to a predetermined position in a direction to go away from the rotational axis and that the reference portion of the movable body and the position adjusting reference member are held in contact, the control device controls the at least one drive mechanism to adjust the position of the cutting blade relative to the rotational axis by changing the relative position between the tool spindle and the position adjusting reference member in a direction to come close to each other.