A machine tool operative as both a chucking type lathe and as a horizontal spindle machine center comprises a rotatable spindle horizontally journaled to a spindlehead vertically reciprocal on a machine tool upright, the upright being slidably mounted for movement on one leg of an "L" shaped bed. A saddle, mounted for movement along the other leg of the bed, carries a table rotatably journaled therein. Affixed to the table is a tailstock which carries both toolholders and workpiece holders. A changer arm, journaled to the spindle for rotation about, and linear movement along, an axis parallel to the axis of spindle rotation is operative, when the upright is moved along the bed to a first changer position, to transfer toolholders and workpiece holders between the spindle and a storage drum journaled to the bed for rotation about an axis parallel to the axis of spindle rotation. The changer arm is also operative, when the upright is moved to a second change position distal from the storage drum and when the saddle is moved and table is rotated, to position the tailstock along the side of the spindle, to transfer toolholders and workpiece holders between the spindle and the tailstock. In this way, a turning operation can be accomplished by transferring a turning tool to the tailstock and a workpiece holder to the spindle. A machining center operation is effectuated by transferring a workpiece holder from the spindle to the tailstock and by transferring a cutting tool from the storage drum to the spindle.