A chassis frame (1) including connection members (13) each configured by a pipe that is connected to a vehicle body frame. Each connection member (13) is provided with an attachment part (2) at an end of the pipe. The attachment part (2) includes a flat attachment face (21) formed by flatly crashing an end of the pipe to form the overlapped portion where a plate of the pipe is overlapped. The flat attachment face (21) is provided on a center in left and right direction of the overlapped portion. A shape of the end of the pipe is a substantially gate shape in its cross section. The attachment part (2) further includes longitudinal ribs (22) bending from the flat attachment face (21) to both left and right sides of the overlapped portion. Each longitudinal rib (22) is formed with a through hole (221) communicating an outside and an inner side of each connection member (13) by expanding a folded edge of the overlapped portion, the through hole is shortened by cutting the plate of the pipe surrounding an opening of the through hole (221).