Metal coating film for electromagnetic wave transmission, method for forming metal coating film for electromagnetic wave transmission, and in-vehicle radar device

Provided is a metal coating film for electromagnetic wave transmission which can be produced inexpensively using a metal other than indium. Also provided are a method for forming a metal coating film for electromagnetic wave transmission, and an in-vehicle radar device. As the metal coating film for electromagnetic wave transmission (100), a catalyst adhesion layer (20) which contains a water-insoluble polyester resin and which is disposed on the surface of a non-conductive base (10) is provided with a metal coating film (3): which is formed in the shape of an island by means of electroless plating; which has, between the islands (31) and in one unit area (1mm 2 ), 1 to 5000 gaps (32) functioning as the transmission path for the electromagnetic wave; and which exhibits metallic luster.