To provide an inexpensive envelope which is mailed as a content delivered remains seen through, and a receiving person can check the content immediately.

The content see-through envelope seals a content including an address-written paper piece by a rectangular base paper and a permeable base material of substantially the same size and sends the content. An adhesive layer is formed at least on a part of one side of the base paper, and the base paper and the permeable base material are bound at a binding part formed along one end of a rectangle.