To easily form the hollow part of a flowing passage etc., into the inner part of an aluminum cast body and to easily reuse a waste material of the aluminum cast body.

In the aluminum cast product forming the hollow part of the flowing passage 20 etc., of fluid into the inner part of the cast body which integrally inserts an insert material 24 formed with the aluminum or the aluminum alloy with the aluminum cast body, a material artificially forming an aluminum oxide film on the surface as the insert material 24, is used. As a method for forming the oxide film on the surface of the insert material 24, an anodic oxidizing method of aluminum is utilized.