A seal member for sealing the developer container at a boundary between the developer container and a developer carrying member is disposed at an opening of a developer container containing developer. The sealing member includes a warp pile fabric, and is formed by a V pile weave providing a V-shaped pile fabric texture. The seal member has a fiber density, representing a number of fibers per unit area, of not less than 260,000/inch.sup.2 and not more than 680,000/inch.sup.2 and has a number of denier per one pile of not less than 200 denier and not more than 350 denier.