A back board attachment structure for a seat back having a trim cover , a back board and a first folding portion (5a1, 5Aa1) in which an edge portion on said back surface side of said trim cover is folded back, a first fastener having a first element (7a2, 7Aa2), in which said first element (7a2, 7Aa2) is attached to said first folding portion (5a1, 5Aa1), a second folding portion (6a1, 6Aa1) in which an edge portion to be said backrest surface side of said back board is folded back, and a second fastener having a second element (7b2, 7Ab2), in which said second element (7b2, 7Ab2) is attached to said second folding portion (6a1, 6Aa1), wherein said first fastener and said second fastener are made to be capable of engaging one another, and wherein - said back board is configured by including a hard base material portion and a skin portion provided to cover one surface of said base material portion , said skin portion has a skin extended portion (6d1, 6Ad1) that is extended by protruding from an edge portion of said base material portion , and said second folding portion (6a1, 6Aa1) is formed on said skin extended portion (6d1, 6Ad1), or - said back board has a soft portion (AS) that is softer than other portions, at an edge portion to be said backrest surface side, said second folding portion (6a1, 6Aa1) is formed by folding said soft portion (AS), and said soft portion (AS) is a weak press portion (AS) having a less amount of compression than the other portions to become softer and thicker. a first folding portion (5a1, 5Aa1) in which an edge portion on said back surface side of said trim cover is folded back, a first fastener having a first element (7a2, 7Aa2), in which said first element (7a2, 7Aa2) is attached to said first folding portion (5a1, 5Aa1), a second folding portion (6a1, 6Aa1) in which an edge portion to be said backrest surface side of said back board is folded back, and a second fastener having a second element (7b2, 7Ab2), in which said second element (7b2, 7Ab2) is attached to said second folding portion (6a1, 6Aa1), wherein said first fastener and said second fastener are made to be capable of engaging one another, and wherein - said back board is configured by including a hard base material portion and a skin portion provided to cover one surface of said base material portion , said skin portion has a skin extended portion (6d1, 6Ad1) that is extended by protruding from an edge portion of said base material portion , and said second folding portion (6a1, 6Aa1) is formed on said skin extended portion (6d1, 6Ad1), or - said back board has a soft portion (AS) that is softer than other portions, at an edge portion to be said backrest surface side, said second folding portion (6a1, 6Aa1) is formed by folding said soft portion (AS), and said soft portion (AS) is a weak press portion (AS) having a less amount of compression than the other portions to become softer and thicker. - said back board is configured by including a hard base material portion and a skin portion provided to cover one surface of said base material portion , said skin portion has a skin extended portion (6d1, 6Ad1) that is extended by protruding from an edge portion of said base material portion , and said second folding portion (6a1, 6Aa1) is formed on said skin extended portion (6d1, 6Ad1), or - said back board has a soft portion (AS) that is softer than other portions, at an edge portion to be said backrest surface side, said second folding portion (6a1, 6Aa1) is formed by folding said soft portion (AS), and said soft portion (AS) is a weak press portion (AS) having a less amount of compression than the other portions to become softer and thicker. <EOS>