A developer accommodating apparatus includes a developer accommodating portion for accommodating a developer; developer detecting means, including a light receiving element for receiving light emitted by a light emitter, for detecting the developer in said developer accommodating portion; a cylindrical light guide member, provided projected from a side surface of said developer accommodating portion, for guiding the light emitted from said light emission element to said light receiving element; a rotatable member provided on a peripheral surface of said light guide member and rotatable about said light guide member; and driving means for rotating said rotatable member.