To provide a catalyst module structure of a high temperature denitrification apparatus which can prevent buckling in the outer plate of a cylindrical unit in the catalyst module due to drastic temperature changes on initiating the process and which can prevent damages in the catalyst.

The catalyst module 12 is constituted by attaching an outer plate 16 which can slide on thermal expansion to an outer frame 15 comprising assembled square steel tubes 13 and L-shape steels 14 to obtain a top panel, base panel and side pane 19 as outer frame panels, assembling the top panel, base panel and side panel 19 as outer frame panels to make a cylindrical unit 20 having openings in the front and rear faces, and filling the inside of the cylindrical unit 20 with a catalyst 21 by supporting the catalyst by the outer frames 15.