Abstract: A bonded body obtained by unifying a plurality of structural members exhibiting 0.6*10?6/K or less of absolute value of thermal expansion coefficient in room temperature, 100 GPa or more of modulus of elasticity and 40 GPa·cm3/g or more of specific rigidity, the plurality of structural members having bonding surfaces that are brought into contact with each other and are unified by a heating process, and a manufacturing method thereof are provided. The sintered block contains 51.5 to 70.0 oxide-equivalent mass % of Si, the oxide-equivalent mass % being calculated as a ratio of Si in elements (Mg, Al and Si) constituting the sintered block on oxide (MgO, Al2O3, SiO2) basis. Surplus SiO2 residing in the sintered block forms a liquid phase during the heating process to activate mass transfer, so that the material of the bonded portion becomes substantially the same as the base material.