Abstract: A transmission-line holding device comprises: a base, being a U-shaped base encircling a semi-opened internal space which is constructed from a horizontal board and a pair of vertical boards; a terminal positioning structure, settled between the two vertical boards for positioning the terminal connectors at a front end and a rear end of the transmission line inside of the internal space of the base; and a mating structure, arranged behind each of the terminal connectors of the transmission line, respectively. Thereupon, the terminal connectors can be retained inside of the base by coupling the mating structures and the terminal positioning structure mutually, so as to provide the advantages of getting the transmission line ordered, stored, and carried conveniently.