A developing device and image forming apparatus are provided. The developing device includes a chassis; a developer carrying member; a thickness regulating member; a supply member; and a conveying member. In a state in which the developing device is attached to a main body an opening of the chassis faces upward; the thickness regulating member pressure-contacts the developer carrying member from below the developer carrying member; the conveying member is disposed below the developer carrying member; the supply member overlaps a portion of the conveying member in a horizontal direction; and a portion of the conveying member is disposed within a vertical projection plane between a pressure-contact position of the thickness regulating member to the developer carrying member, and a contact position of the supply member to the developer carrying member. The image forming apparatus includes a main body; a plurality of photosensitive members; and a plurality of developing devices.