Provided are: a resin-containing sheet in which not only the mechanical strength of a cellulose nanofiber nonwoven fabric but also the flexural resistance of a substrate are improved; and a structure and a wiring board which include the same. The resin-containing sheet includes: a specific cellulose nanofiber nonwoven fabric (11); a fixing agent (2) which fixes together fibers (1) in the cellulose nanofiber nonwoven fabric (11); and a resin (3) which is in contact with the cellulose nanofiber nonwoven fabric (11) and the fixing agent (2), wherein the storage modulus of the fixing agent (2) is higher than that of the resin (3). The structure is obtained by tightly adhering the resin-containing sheet to a substrate. The wiring board includes this structure.