The blade back seal and the sponge sealing member are interposed between the leaf spring member and the blade attachment unit and seal arrangement portion while being compressed to have the same thickness, by applying the blade back seal having a relatively small elastic modulus and a large thickness to the blade attachment unit and the seal arrangement portion, applying the sponge sealing member having a relatively large elastic modulus and a small thickness onto the roller opposed face of the seal arrangement portion and pressing them by the leaf spring member of the blade unit.