A breathable salt core is provided that is placed in a cavity of a casting mold in order to mold a hollow part of a cast product and that is dissolved and removed after casting, the breathable salt core being formed by powder molding innumerable salt particles into a predetermined shape corresponding to the hollow part, wherein a gap that can retain a gas remaining in the cavity in a casting process is formed between the innumerable salt particles that have been powder molded. The breathable salt core thus manufactured assures that residual gas within the cavity pushed by the molten metal to enter the gap formed between salt particles of the salt core, thereby avoiding any incomplete filling of the molten metal, and which can be formed with a simple production process at a low cost.