A holding structure is provided for an option connector that is mounted at an end of a branch line of a wire harness of a vehicle. A fixing part is defined at an area of the branch line separated from the option connector by a predetermined distance. A holding part is provided on a peripheral component of the vehicle that is in a vicinity of the wire harness. The holding part is configured for releasably holding the fixing part of the branch line so that a tip area of the branch line that begins at the fixing part and includes the option connector extends out from the holding part.