An electronic device, comprising: a first housing; a second housing; a hinge structure foldably coupling at least part of the first housing with at least part of the second housing, to support folding and unfolding operations; a flexible display disposed over the first housing, the second housing, and the hinge structure; a hinge housing in which at least part of the hinge structure is seated; a first member disposed on at least part of a periphery of the first housing that is adjacent to at least part of the second housing when the first housing and the second are set in a flat unfolded state; and a second member disposed on at least part of a periphery of the second housing that at least part of the first housing faces when the first housing and the second housing are set in the flat unfolded state; characterized in that the electronic device further comprises a supplementary structure at least partially fastened to an edge portion of the hinge housing to reduce a gap between the flexible display and the hinge housing, wherein the supplementary structure includes: a fixing bracket coupled to the hinge housing; a first wing part coupled to the fixing bracket, and disposed between the first member and the first housing; a second wing part coupled to the fixing bracket, and disposed between the second member and the second housing; and a coupling part coupling the first wing part and the second wing part to the fixing bracket. a first housing; a second housing; a hinge structure foldably coupling at least part of the first housing with at least part of the second housing, to support folding and unfolding operations; a flexible display disposed over the first housing, the second housing, and the hinge structure; a hinge housing in which at least part of the hinge structure is seated; a first member disposed on at least part of a periphery of the first housing that is adjacent to at least part of the second housing when the first housing and the second are set in a flat unfolded state; and a second member disposed on at least part of a periphery of the second housing that at least part of the first housing faces when the first housing and the second housing are set in the flat unfolded state; characterized in that the electronic device further comprises a supplementary structure at least partially fastened to an edge portion of the hinge housing to reduce a gap between the flexible display and the hinge housing, wherein the supplementary structure includes: a fixing bracket coupled to the hinge housing; a first wing part coupled to the fixing bracket, and disposed between the first member and the first housing; a second wing part coupled to the fixing bracket, and disposed between the second member and the second housing; and a coupling part coupling the first wing part and the second wing part to the fixing bracket. a fixing bracket coupled to the hinge housing; a first wing part coupled to the fixing bracket, and disposed between the first member and the first housing; a second wing part coupled to the fixing bracket, and disposed between the second member and the second housing; and a coupling part coupling the first wing part and the second wing part to the fixing bracket.