In a machine for forming articles of sheet material, an orderly succession of flat blanks is fed along a forming path on a roller conveyor having powered rollers equally spaced with a given spacing; on the roller conveyor, the blanks are maintained contacting the rollers by idle-wheel pressure devices, and are deformed by folding devices; the pressure devices and folding devices being fitted to respective gantry-type frames having respective removable cross members, and which can be set to a number of predetermined reference positions and locked in such positions releasably with respect to the roller conveyor; and a continuous guide and slide adjusting assembly being interposed between each frame and the respective pressure devices and folding devices to adjust the position of the devices on the roller conveyor as a function of the shape and size of the blanks.