A long synthetic resin foam body comprising: a thermoplastic resin expanded beads-molded substrate that has a longitudinal direction, a lateral direction and a thickness direction, and a frame that has a pair of displacement regulating sections which are longitudinally or laterally spaced apart from each other and provided in said substrate at positions spaced inward from opposing longitudinal or lateral ends of said substrate and at least one connecting section which connects the paired displacement regulating sections to each other, said substrate having at least one joint forming portion that divides said substrate in a direction intersecting the connecting section into two or more substrate parts (10, 11), said joint forming portion having at least one joint which connects adjacent two substrate parts (10, 11) to each other and which has one end connected to one of adjacent two substrate parts (10, 11) at a first connecting location and the other end connected to the other one of the substrate parts (10,11) at a second connecting location, characterized in that said second connecting location is positioned to be offset from said first connecting location in at least two directions selected from the longitudinal direction, lateral direction and thickness direction or to be aligned with said first connecting location in all of the longitudinal direction, lateral direction and thickness direction with said joint being formed into a curved or bent shape, sc that said joint is deformable to permit a relative displacement between the adjacent two substrate parts (10, 11) when said substrate contracts or expands. a thermoplastic resin expanded beads-molded substrate that has a longitudinal direction, a lateral direction and a thickness direction, and a frame that has a pair of displacement regulating sections which are longitudinally or laterally spaced apart from each other and provided in said substrate at positions spaced inward from opposing longitudinal or lateral ends of said substrate and at least one connecting section which connects the paired displacement regulating sections to each other, said substrate having at least one joint forming portion that divides said substrate in a direction intersecting the connecting section into two or more substrate parts (10, 11), said joint forming portion having at least one joint which connects adjacent two substrate parts (10, 11) to each other and which has one end connected to one of adjacent two substrate parts (10, 11) at a first connecting location and the other end connected to the other one of the substrate parts (10,11) at a second connecting location, characterized in that said second connecting location is positioned to be offset from said first connecting location in at least two directions selected from the longitudinal direction, lateral direction and thickness direction or to be aligned with said first connecting location in all of the longitudinal direction, lateral direction and thickness direction with said joint being formed into a curved or bent shape, sc that said joint is deformable to permit a relative displacement between the adjacent two substrate parts (10, 11) when said substrate contracts or expands.