For inserting terminals into each connector housing and reducing working area in processes by eliminating rearrangement of wires with terminals, a manufacturing method for wiring harnesses, including the steps of: picking up both ends of a wire at a predetermined position in a transferring direction from a transferring device by a pair of chucks, each chuck picking up one of the both ends of the wire; chucking the both ends of the wire with terminals fed through the pair of chucks, each end of the wire being fed through one of the pair of chucks, by a pair of terminal inserting heads as the terminal inserting device, the pair of terminal inserting heads moving freely independently of each other at least in a direction of a row of a connector housings; and inserting the terminals at the both ends simultaneously into each of the connector housings.