To provide a transmission path with little loss even when a signal at a frequency of over 8 GHz is transmitted. In a transmission path 12 transmitting high-frequency signals each containing a frequency component of over 8 GHz, the transmission path 12 includes a nickel-phosphorus layer 122 containing nickel and phosphorus, and a phosphorus concentration of the nickel-phosphorus layer 122 is over 0 mass% and less than 8 mass%. Such a structure enables to provide a transmission path with little loss even when a signal at a frequency of over 8 GHz is transmitted.