A gear grinding machine wherein a tooth alignment operation is performed prior to grinding, is equipped with a workpiece processing rotation shaft (22) which rotates a workpiece (W1) located at a workpiece processing position (P2); a workpiece swing device (30) whereby a tailstock (50) that holds the workpiece (W1) is swung between a workpiece replacement position (P1) and a workpiece processing position; a workpiece alignment rotation shaft (52) which rotates the workpiece held by the tailstock (50); and a tooth alignment sensor (43) that detects the rotation phase of the workpiece, which was rotated by the workpiece alignment rotation shaft. Before the workpiece held by the tailstock is placed at the workpiece processing position, the rotation of the workpiece alignment rotation shaft is controlled on the basis of the rotation phase detected, so that the workpiece will engage with a threaded grinding stone (16).