To provide a high strength panel which is used as a floor material of a cleaning facility such as a semiconductor clean room and uniformly disperses load transmitted from an upper part over the whole panel without concentrating to one place while effectively increasing concentration strength at any point and effectively supporting vertical load and eccentric load applied to the whole panel.

The high strength panel includes an edge rib which has at one side a tapered surface that is formed at an edge part of the panel and increases its thickness toward a bottom surface, main reinforcing ribs as a partition wall which are arranged in an internal space of the edge part and has many square grid parts in the internal space and auxiliary reinforcing ribs which are formed in the internal space of the grid part and partitions the inside of the grid part in a grid state. A plurality of circular grooves for reinforcing supporting force relative to the vertical load and the eccentric load applied from the upper part are formed at each bottom part of the respective grid parts which are partitioned by the respective auxiliary reinforcing ribs.