To provide an opened cell structure for an air filter provided with improved capability of removing object substances to be adsorbed while suppressing increase of pressure loss.

The opened cell structure is composed of a large number of air flow paths which are surrounded with a filtration material sheet containing a gas adsorbent and a thermoplastic resin and accumulated in parallel and the opened cell structure has 20% or higher aperture ratio in the transverse cross-section rectangular to the air flow paths, 0.35 g/cm3 or higher density of the filtration material sheet, and 1.0 m2/L or wider cell surface area per unit volume of the opened cell structure itself.