Machining apparatus and machining method

A machining apparatus, comprising:

• a workpiece retainer that retains a workpiece having a noncircular peripheral surface;
• a workpiece spindle having an attachment portion to which the workpiece retainer is attached;
• an adjustment unit that adjusts a retaining force between the workpiece and the workpiece retainer;
• a phase determination member that is placed in a rotation range of the workpiece, and that determines a phase of the workpiece as the workpiece is rotated so that the peripheral surface contacts the phase determination member and the workpiece rotates relative to the workpiece retainer;
• a phase determination detection unit that detects completion of the phase determination;
• a control unit that controls the adjustment unit so that the retaining force is a retaining force for phase determination until the phase determination is completed, and the retaining force is switched to a retaining force for machining which is larger than the retaining force for phase determination after the phase determination is completed, and that uses a phase of the workpiece spindle at the time the phase determination is completed as a machining reference phase;
• and
• a machining unit that machines the workpiece by using the machining reference phase as a reference.