Machine for forming ceramic articles, comprising: - a bearing structure intended to be positioned on the ground; - forming means associated with said bearing structure, provided with at least one supporting surface intended to support the material to be formed and with at least one pressing element which is movable close to/away from said supporting surface, where said pressing element consists of the mobile part of a fluid-operated cylinder the body of which is associated integral with said bearing structure; - stiffening means associated in a removable manner with said bearing structure; wherein said bearing structure has a pair of lateral faces, arranged transversely to said supporting surface and mutually opposite, and has at least one access opening to the supporting surface itself which faces at least one of said lateral faces, and wherein said stiffening means comprise at least one pair of stiffening elements each of which being connected and associated in a removable manner with said bearing structure at at least one of said lateral faces and comprise fixing means of said stiffening elements to said bearing structure, where said fixing means comprise one or more first threaded elements which connect the stiffening elements together which are associated with said opposite lateral faces, passing through said bearing structure, and tightening means of said threaded members and where said bearing structure and said stiffening elements comprise one or more first through holes for inserting said first threaded elements; characterized by the fact that said stiffening elements comprise at least one through opening which faces said access opening and wherein said through opening defines at least one upper edge, which rests, in use, on top of the body of said cylinder, and at least one lower edge mechanically connectable to said bearing structure, and by the fact that it comprises second threaded elements which connect said bearing structure to the lower edge of each of said stiffening elements, said lower edge comprising one or more second holes for inserting said second threaded elements. - a bearing structure intended to be positioned on the ground; - forming means associated with said bearing structure, provided with at least one supporting surface intended to support the material to be formed and with at least one pressing element which is movable close to/away from said supporting surface, where said pressing element consists of the mobile part of a fluid-operated cylinder the body of which is associated integral with said bearing structure; - stiffening means associated in a removable manner with said bearing structure; wherein said bearing structure has a pair of lateral faces, arranged transversely to said supporting surface and mutually opposite, and has at least one access opening to the supporting surface itself which faces at least one of said lateral faces, and wherein said stiffening means comprise at least one pair of stiffening elements each of which being connected and associated in a removable manner with said bearing structure at at least one of said lateral faces and comprise fixing means of said stiffening elements to said bearing structure, where said fixing means comprise one or more first threaded elements which connect the stiffening elements together which are associated with said opposite lateral faces, passing through said bearing structure, and tightening means of said threaded members and where said bearing structure and said stiffening elements comprise one or more first through holes for inserting said first threaded elements; characterized by the fact that said stiffening elements comprise at least one through opening which faces said access opening and wherein said through opening defines at least one upper edge, which rests, in use, on top of the body of said cylinder, and at least one lower edge mechanically connectable to said bearing structure, and by the fact that it comprises second threaded elements which connect said bearing structure to the lower edge of each of said stiffening elements, said lower edge comprising one or more second holes for inserting said second threaded elements.