A filter pack comprising: a filter medium that is configured to collect fine particles in a gas and that a pleating is performed such that mountain folds and valley folds are alternately repeated; and a plurality of spacing members that maintain a distance between adjacent mountain-folded portions or adjacent valley-folded portions of the filter medium, and are each formed of a thermoplastic resin adhesive that is in a solidified state, wherein the filter medium includes two extension portions (11a, 11b) that extend to both sides of folds of the filter medium that are formed through the pleating, the extension portions (11a, 11b) facing each other in a state where the filter medium is folded, the plurality of spacing members (11a, 11b) include paired spacing members that are respectively provided on the extension portions (11a, 11b) so as to linearly extend in a direction that is orthogonal to the folds, the paired spacing members are in contact with each other in the state where the filter medium is folded, and characterized in that surfaces of the paired spacing members that come into contact with each other each include a flat surface that extends in a direction that is orthogonal to a direction in which the spacing members face each other when viewed in an extending direction of the spacing members, wherein when viewed in the extending direction of the spacing members, a width of each of the spacing members along a direction that is parallel to an extending direction of the flat surface of the spacing member is maximum at a bottom surface of the spacing member that is in contact with the filter medium, wherein in a direction that is parallel to the extending direction of the flat surface, a located position of the flat surface is within the range of a located position of the bottom surface, and the width of the spacing member that includes the flat surface becomes shorter in a direction away from the bottom surface. a filter medium that is configured to collect fine particles in a gas and that a pleating is performed such that mountain folds and valley folds are alternately repeated; and a plurality of spacing members that maintain a distance between adjacent mountain-folded portions or adjacent valley-folded portions of the filter medium, and are each formed of a thermoplastic resin adhesive that is in a solidified state, wherein the filter medium includes two extension portions (11a, 11b) that extend to both sides of folds of the filter medium that are formed through the pleating, the extension portions (11a, 11b) facing each other in a state where the filter medium is folded, the plurality of spacing members (11a, 11b) include paired spacing members that are respectively provided on the extension portions (11a, 11b) so as to linearly extend in a direction that is orthogonal to the folds, the paired spacing members are in contact with each other in the state where the filter medium is folded, and characterized in that surfaces of the paired spacing members that come into contact with each other each include a flat surface that extends in a direction that is orthogonal to a direction in which the spacing members face each other when viewed in an extending direction of the spacing members, wherein when viewed in the extending direction of the spacing members, a width of each of the spacing members along a direction that is parallel to an extending direction of the flat surface of the spacing member is maximum at a bottom surface of the spacing member that is in contact with the filter medium, wherein in a direction that is parallel to the extending direction of the flat surface, a located position of the flat surface is within the range of a located position of the bottom surface, and the width of the spacing member that includes the flat surface becomes shorter in a direction away from the bottom surface.