A CNC machine tool includes a worktable supporting two workpieces and rotatable on a base so as to exchange the positions of the workpieces. A post member is fixed on the base. A first horizontal rail unit is movable vertically on the post member. A second horizontal rail unit is movable on the first horizontal rail unit along a first horizontal direction. A spindle head unit is movable on the second horizontal rail unit along a second horizontal direction perpendicular to the first horizontal direction.