Two press cylinders are disposed at an equal interval at left and right having the opening-closing cylinder therebetween, so as to have the approximately same distance from the conveying reference plane as the opening-closing cylinder. The opening-closing cylinder comprises an opening-closing linear encoder, which detects a decreased amount of the entire thickness of the object-to-be-processed as a displacement of the ram, when the object-to-be-processed is hot-pressed. The respective press cylinders comprise pressure sensors for press cylinders detecting pressing pressures of the pressing plates as cylinder inner pressures. A horizontal hotpress system is provided, which can easily improve yield ratio of the boards after hot-pressing by measuring thickness size of the object-to-be-processed while hot-pressed, according to an operation distance of the opening-closing cylinder, comprising an opening-closing cylinder for opening and closing the press plates, other than a plurality of the press cylinders for pressing the press plates.