Hollow casting and manufacturing method therefor, and method and apparatus for smoothing internal surface of hollow casting

There is provided a hollow casting in which a surface roughness Ra of a casting wall portion surface forming a hollow portion formed by a wall portion is 10 mum or less. Such a hollow casting can be obtained by a manufacturing method for the hollow casting in which after molten metal is poured into a mold to be molded by casting, processing of removing residual matters on the casting wall portion surface forming the hollow portion and processing of smoothing the casting wall portion surface forming the hollow portion are performed at the same time under predetermined conditions. According to the present invention, a casting which has the hollow portion formed by the wall portion and whose wall portion surface forming the hollow portion is very smooth and which has a low passage resistance can be manufactured at a lower cost without increasing an environmental load in the manufacturing process.