A chair characterized by: a frame including a coupling member; and a seat-forming assembly including first and second plate members (21, 21') that serve respectively as a seat and a backrest of said chair, each of said first and second plate members (21, 21') having a connecting portion and a hook-mounting portion that is opposite to said connecting portion, a linking member that links said connecting portions of said first and second plate members (21, 21') together, and a hook unit that includes a plurality of first hooks connected to said hook-mounting portion of said first plate member, and a plurality of second hooks connected to said hook-mounting portion of said second plate member, said first and second hooks (230, 230') being capable of detachably engaging said coupling member of said frame, wherein said coupling member has curved first and second coupling portions (151, 152) opposite to each other, said hook-mounting portion of each of said first and second plate members (21, 21') being proximate to a respective one of said first and second coupling portions (151, 152), and having a curvature that substantially equals that of the respective one of said first and second coupling portions (151, 152); wherein said connecting portion of each of said first and second plate members (21, 21') is formed with a plurality of spaced-apart through holes, and said linking member is a rope extending through said through holes; and wherein each of said first and second hooks (230, 230') of said hook unit has a hook body that defines a groove receiving removably a corresponding one of said first and second coupling portions (151, 152) of said coupling member of said frame, and an opening communicating said groove and having a width smaller than a diameter of the corresponding one of said first and second coupling portions (151, 152) of said coupling member. a frame including a coupling member; and a seat-forming assembly including first and second plate members (21, 21') that serve respectively as a seat and a backrest of said chair, each of said first and second plate members (21, 21') having a connecting portion and a hook-mounting portion that is opposite to said connecting portion, a linking member that links said connecting portions of said first and second plate members (21, 21') together, and a hook unit that includes a plurality of first hooks connected to said hook-mounting portion of said first plate member, and a plurality of second hooks connected to said hook-mounting portion of said second plate member, said first and second hooks (230, 230') being capable of detachably engaging said coupling member of said frame, first and second plate members (21, 21') that serve respectively as a seat and a backrest of said chair, each of said first and second plate members (21, 21') having a connecting portion and a hook-mounting portion that is opposite to said connecting portion, a linking member that links said connecting portions of said first and second plate members (21, 21') together, and a hook unit that includes a plurality of first hooks connected to said hook-mounting portion of said first plate member, and a plurality of second hooks connected to said hook-mounting portion of said second plate member, said first and second hooks (230, 230') being capable of detachably engaging said coupling member of said frame, wherein said coupling member has curved first and second coupling portions (151, 152) opposite to each other, said hook-mounting portion of each of said first and second plate members (21, 21') being proximate to a respective one of said first and second coupling portions (151, 152), and having a curvature that substantially equals that of the respective one of said first and second coupling portions (151, 152); wherein said connecting portion of each of said first and second plate members (21, 21') is formed with a plurality of spaced-apart through holes, and said linking member is a rope extending through said through holes; and wherein each of said first and second hooks (230, 230') of said hook unit has a hook body that defines a groove receiving removably a corresponding one of said first and second coupling portions (151, 152) of said coupling member of said frame, and an opening communicating said groove and having a width smaller than a diameter of the corresponding one of said first and second coupling portions (151, 152) of said coupling member.