A machine tool comprises: a workpiece spindle (12) having an electromagnetic chuck (18) provided on an upper end thereof for clamping a workpiece (W), and extending along the Z-axis; a tool magazine which accommodates a tool (T) and a centering jig (20); an automatic tool changer (17) for exchanging the tool (T) between the tool magazine and a tool spindle; and a run-out measuring device (19) for measuring a run-out of the workpiece (W) placed on the electromagnetic chuck (18); wherein a workpiece correction distance is calculated on the basis of the run-out of the workpiece (W) measured by the run-out measuring device (19) before the workpiece (W) is clamped by the electromagnetic chuck (18), and a workpiece centering operation is automatically performed by the centering jig (20) attached to the tool spindle until the run-out of the workpiece (W) falls within an allowable range.