A seal member for sealing an opening of a developer accommodating container for accommodating a developer, which developer accommodating container is detachably mountable to a main assembly of an image forming apparatus, includes a seal base for sealing the opening; a force receiving portion for receiving a force for unsealing the seal base; an electroconductive portion capable of being disconnected by an unsealing operation of the seal base, the electroconductive portion including a contact portion electrically connectable with a contact portion of the main assembly of the image forming apparatus to permit the main assembly of the image forming apparatus to detect whether the electroconductive portion is disconnected or not.