A seat post device, the seat post device having an elongated seat post body and a seat post connector mounted on the seat post body, characterized in that: the seat post body comprises a cross section being non-circular; a windward side; a leeward side; a left side; a right side; and a combining end defined as a top end of the seat post body and comprising a top surface; and two combining holes formed at an interval in the combining end from the top surface of the combining end; and the seat post connector is combined with and selectively turned relative to the combining end, and comprises a top side; a bottom side abutting the combining end; a first side; a second side, wherein the first side and the second side of the seat post connector correspond in position to the right side and the left side of the seat post body respectively; a first end; a second end, wherein the first end and the second end correspond in position to the windward side and the leeward side respectively; two seat post holes formed through the seat post connector from the top side to the bottom side of the seat post connector and aligning with the combining holes respectively; two bolts inserted into the seat post holes and then into the combining holes such that the seat post connector is combined with the combining end; a saddle fixing hole being rounded and formed through the seat post connector from the first side to the second side of the seat post connector; and a saddle adjusting hole being curved and formed through the seat post connector from the first side to the second side of the seat post connector. the seat post body comprises a cross section being non-circular; a windward side; a leeward side; a left side; a right side; and a combining end defined as a top end of the seat post body and comprising a top surface; and two combining holes formed at an interval in the combining end from the top surface of the combining end; and a cross section being non-circular; a windward side; a leeward side; a left side; a right side; and a combining end defined as a top end of the seat post body and comprising a top surface; and two combining holes formed at an interval in the combining end from the top surface of the combining end; and a top surface; and two combining holes formed at an interval in the combining end from the top surface of the combining end; and the seat post connector is combined with and selectively turned relative to the combining end, and comprises a top side; a bottom side abutting the combining end; a first side; a second side, wherein the first side and the second side of the seat post connector correspond in position to the right side and the left side of the seat post body respectively; a first end; a second end, wherein the first end and the second end correspond in position to the windward side and the leeward side respectively; two seat post holes formed through the seat post connector from the top side to the bottom side of the seat post connector and aligning with the combining holes respectively; two bolts inserted into the seat post holes and then into the combining holes such that the seat post connector is combined with the combining end; a saddle fixing hole being rounded and formed through the seat post connector from the first side to the second side of the seat post connector; and a saddle adjusting hole being curved and formed through the seat post connector from the first side to the second side of the seat post connector. a top side; a bottom side abutting the combining end; a first side; a second side, wherein the first side and the second side of the seat post connector correspond in position to the right side and the left side of the seat post body respectively; a first end; a second end, wherein the first end and the second end correspond in position to the windward side and the leeward side respectively; two seat post holes formed through the seat post connector from the top side to the bottom side of the seat post connector and aligning with the combining holes respectively; two bolts inserted into the seat post holes and then into the combining holes such that the seat post connector is combined with the combining end; a saddle fixing hole being rounded and formed through the seat post connector from the first side to the second side of the seat post connector; and a saddle adjusting hole being curved and formed through the seat post connector from the first side to the second side of the seat post connector.