To provide a method capable of readily forming a latex layer, while keeping the shape of the bag body, when the latex layer is formed in the inner part of the bag body.

A latex coagulant is applied to the inner part of the bag body B, the ambient atmosphere of the bag body is reduced in pressure and a latex solution is poured to the inside of the bag body. Since the bag body is placed in pressure-reduced atmosphere, the bag body is inflated by the inner pressure. The latex layer is formed, as the bag is inflated and a latex bag body can be readily formed in a variety of prescribed shapes.