A long synthetic resin foam body composed of a thermoplastic resin expanded beads-molded substrate and a frame having displacement regulating sections provided at both ends in the longitudinal or lateral direction of the substrate and a connecting section that connects the displacement regulating sections to each other. The substrate has at least one joint forming portion that divides the substrate in a direction intersecting the connecting section into two or more substrate parts. The joint forming portion has a joint that connects the adjacent two substrate parts to each other and is deformable to permit a relative displacement between the adjacent two substrate parts when the substrate contracts or expands.