To provide a seat having a three-dimensional complex undulated cushion body securing hardness in a stress direction and excelling in dispersibility of the stress and durability, and a method of manufacturing the same.A seat 1 includes frames (15, 25), cushion bodies (11, 21) obtained by forming a plurality of sheet-like fibrous structures 4a to 4d integrally, and covers (13, 23), wherein a sheet-like fibrous structure 4 is formed by performing cotton blending of thermally adhesive composite short fibers to inelastic crimped short fibers and thermally adhering crossing points, and the sheet-like fibrous structure 4 satisfies a relationship of A≧3B/2 when the number of short fibers arranged along a thickness direction is represented as A and the number of short fibers arranged along a direction perpendicular to the thickness direction is represented as B, and the cushion bodies 11, 21 are obtained by disposing in a state in which the sheet-like fibrous structures 4a to 4d are stacked and compressed in a mold 40, and forming the sheet-like fibrous structures 4a to 4d integrally by performing high pressure steam molding, and provided on the frames 15, 25 such that a thickness direction extends along a direction in which a load is applied.