Provided is an interlocking chain unit configured such that chains reliably and firmly engage with each other and that the buckling and twisting of a rigidified chain portion are avoided. An interlocking chain unit (100) is configured such that the outer edges of a plate overlap region (P) are defined by contact portion faces (111aa, 111aa) and flat buckling restricting end faces (112b, 112b), and that the plate overlap region (P) is constructed from the outlines of two plate overlap portions (Pa, Pa) which are point-point-symmetric about the point (C) of intersection between hook-shaped interlocking end faces (111a, 111a) and the buckling restricting end faces (112b, 112b).