In a machine tool, a column base (12) is supported on a bed (11) movably in a horizontal direction, and a column (13) is installed vertically on the column base (12). A saddle (14) is supported on a side of the column (13) movably in a vertical direction, and a ram stock (15) is supported on the saddle (14) movably in a horizontal direction. A main spindle (16) is rotatably supported by the ram stock (15). A weight (22) is supported in the column (13) movably in a direction parallel to the ram stock (15), so that the weight (22) can be moved horizontally by a servo motor (23). An NC device (25) moves the weight (22) by the servo motor (23) synchronously with a movement of the ram stock (15), to adjust balance of the column (13), thereby enabling to reduce the size of an apparatus and realize space saving.