A developing device includes: a storage part in which a developer is stored; a transport body that includes a spiral blade and transports the developer via a rotation thereof; a developing body to which the developer is supplied from the transport body; an attachment part which is disposed between the transport body and the developing body and includes an opening allowing the developer supplied from the transport body to the developing body to pass and to which a sealing member sealing the opening is detachably attached; and a connection portion which extends to cross the opening at a spiral angle of the blade as viewed from the developing body toward the transport body and of which one end portion and the other end portion are connected to the attachment part.