The tool set has a horizontally slidable upper side plate tool (4) and a horizontally slidable folding side plate tool (3) for folding a sheet in two opposite folding directions. The tools are so arranged that there is no need to turn the sheet for making a second fold. The upper side plate tool can be slid horizontally along a pivot point D of the machine by at least one pressure medium operated drive cylinder (7). The folding side plate tool can be slid along D by at least one pressure medium operated counter recoil cylinder (14). The upper side plate tool is guided in guide slits (6',6'') of an upper side plate tool support (6).
