A developing apparatus is accommodated within a laser printer. The developing apparatus includes a developing casing and a toner electric field transport body. The toner electric field transport body includes a transport wiring substrate and a transport-substrate support member. A plurality of transport electrodes are provided on the transport wiring substrate. The transport wiring substrate is supported by the transport-substrate support member in a state in which the transport wiring substrate is deformed in a tubular shape. Further, the transport wiring substrate is supported by the transport-substrate support member such that margin areas of the transport wiring substrate, which are opposite end portions of the transport wiring substrate with respect to a sub-scanning direction and in which the transport electrodes are not formed, are separated from a tonner transport path.