A connection structure is provided which, without increasing manufacturing costs, solidly connects a support column to which legs are attached and a seat support which supports the seat body, and which, in a connected state, does not result in rattling or dislodgement of the support column and the seat support; also provided is a chair which is provided with such a connection structure. In this connection structure (30) between a support column (2) and a seat support of a chair, in a concave support column receiving part (42) of a seat receiving main body (4), a window (48), in which a window edge (52) appears, is formed in a concave conical surface (46) of the inner surface of said support column receiving part (42). Part of the window edge (52) is an edge portion (52a) which, due to a load from the seat receiving main body (4) side, bites into the convex conical surface (32) of a seat body attachment part (31), which is the leading end of the support column (2). When the load acts on the seat receiving main
