A portal-type milling-boring machine has two columns disposed on opposite sides of a bed over which a workpiece-supporting table moves, a beam extending between the two columns over said bed. Working heads are carried by the columns and the beam for effecting different machining operations on a workpiece, and the columns are movable on respective transverse guides parallel to the axis of the beam to vary the effective width of the portal. This enables boring operations to be effected on the sides of the workpiece by the working heads carried by the columns. Suspensions are provided for transmitting the weight of the beam and the heads carried thereby to fixed auxiliary columns.