Lathe

A lathe, comprising:

• a spindle which is arranged to rotate freely around an axis line and which holds one end side of an annular workpiece;
• a rotation drive mechanism for rotating the spindle around the axis line;
• and a holding mechanism which is arranged to opposite to the spindle in a manner to be kept apart by an interval in an axial direction of the spindle and which holds the other end side of the workpiece, the lathe configured to machine an outer circumferential surface of the workpiece, wherein
• the holding mechanism, comprises:
• an inserting member which is arranged to rotate freely around a rotational center axis previously set to be coaxially of the axis line of the spindle and of which at least distal end is insertable into an interior of the other end side of the workpiece;
• a support member which supports the inserting member to rotate freely around the rotational center axis;
• a plurality of contact members which are provided to be kept apart by previously set intervals in a circumferential direction of an outer circumference of the distal end of the inserting member and which protrude outwardly to be contactable with an inner circumferential surface of the workpiece;
• and
• a drive mechanism which drives each of the contact members to protrude each of the contact members so as to be brought into contact with the inner circumferential surface of the workpiece, wherein
• each of the contact members is configured to protrude in a state where a protrusion amount reached when each of the contact members contacts the inner circumferential surface of the workpiece differs to each other.