To provide a method for collapsing a pore in the inner part of a casting or a die cast product by which plastic flow deformation is developed by applying partial load on the surface of the casting or the die cast product and the pore existing in the inner part of the product can easily be collapsed.

A part on the surface of the formed product formed with the casting or the die casting is partially pressurized and the plastic deformation is developed in the formed product, and the pore defect formed in the inner part of the formed product is collapsed. In this method, the pore (especially, the pore at a portion near the surface of the product) developed in the inner part of the product can simply be collapsed, and even in the case of performing the machining for cutting off the surface layer of the product with a shaving, or the like, after casting, such problem as to develop the leakage of gas caused by the pore defect in the inner part can be canceled.