An assembly chair comprising: a pair of frames (11, 12) including respective linear side portions (11a, 12a) and curved side portions (11b, 12b), the curved side portions (11b, 12b) being integrally disposed to extend from one end portions of the linear side portions (11a, 12a); a plurality of coupling rods (21, 22, 23) removably mounted between the pair of frames (11, 12); a plurality of pairs of depressed portions disposed at opposed inner surfaces of the pair of frames (11, 12); at least one support member (41, 42, 43) removably mounted between the pair of frames (11, 12) with both end portions of the support member (41, 42, 43) fitted to the depressed portions; and a sheet removably installed in a predetermined manner between the support member (41, 42, 43) and the coupling rod (21, 22, 23) or another support member (41, 42, 43) between the pair of frames (11, 12), wherein at least at one end portion of the sheet, the sheet includes a plurality of insertion portions (61, 62, 63, 64, 65) along a width direction of the sheet, a flat plate (41a, 41b, 41c) being passed through at least a first of the insertion portions (61, 62, 64), the support member (41, 42, 43) with a flat intermediate portion being passed through; a second of the insertion portions (63, 65), the sheet being wound around outer peripheries of the first insertion portion (61, 62, 64) through which the flat plate (41a, 41b, 41c) is passed and the second insertion portion (63, 65) through which the support member (41, 42, 43) with the flat intermediate portion is passed to adjust a length of the sheet, and in such a state, the support member (41, 42, 43) having both end portions fitted to the depressed portions of the frames (11, 12). a pair of frames (11, 12) including respective linear side portions (11a, 12a) and curved side portions (11b, 12b), the curved side portions (11b, 12b) being integrally disposed to extend from one end portions of the linear side portions (11a, 12a); a plurality of coupling rods (21, 22, 23) removably mounted between the pair of frames (11, 12); a plurality of pairs of depressed portions disposed at opposed inner surfaces of the pair of frames (11, 12); at least one support member (41, 42, 43) removably mounted between the pair of frames (11, 12) with both end portions of the support member (41, 42, 43) fitted to the depressed portions; and a sheet removably installed in a predetermined manner between the support member (41, 42, 43) and the coupling rod (21, 22, 23) or another support member (41, 42, 43) between the pair of frames (11, 12), wherein at least at one end portion of the sheet, the sheet includes a plurality of insertion portions (61, 62, 63, 64, 65) along a width direction of the sheet, a flat plate (41a, 41b, 41c) being passed through at least a first of the insertion portions (61, 62, 64), the support member (41, 42, 43) with a flat intermediate portion being passed through; a second of the insertion portions (63, 65), the sheet being wound around outer peripheries of the first insertion portion (61, 62, 64) through which the flat plate (41a, 41b, 41c) is passed and the second insertion portion (63, 65) through which the support member (41, 42, 43) with the flat intermediate portion is passed to adjust a length of the sheet, and in such a state, the support member (41, 42, 43) having both end portions fitted to the depressed portions of the frames (11, 12).