A cushioning member includes: an accommodating bag portion that accommodates a medium; a first fusing portion that defines the accommodating bag portion such that the accommodating bag portion is provided with an opening; a check valve having a first end located inside the accommodating bag portion and a second end located outside the accommodating bag portion, and provided at the opening; a second fusing portion that is immediately adjacent to the first fusing portion on those external sides of the check valve which are opposite in a direction intersecting a direction in which the check valve protrudes from the accommodating bag portion, and defines a channel that communicates with the opening; and a third fusing portion that is connected to the second fusing portion and seals the channel, the third fusing portion being provided across a portion of the check valve that protrudes from the accommodating bag portion.