To provide a composite structure which is obtained by combining a core material and and a surface material consisting of a polycrystalline sintered compact or metal and having a wide difference in thermal expansion coefficients, and in which high hardness and high toughness are made compatible without producing peeling and cracks between the core material and the surface material.

In the composite structure 1 comprising a sintered compact obtained by joining crystal grains 2 and 6 with joining phases 3 and 7 as a long size core material 4 and/or surface material 8, an intermediate layer 9 having a thermal expansion coefficient at the middle between that of the core material 4 and that of the surface material 8 is provided between the core material 4 and the surface material 8.