The flexible metal-cladded base material pertaining to the present invention includes a metal foil and a first resin layer. The first resin layer is of a first resin composition containing a polyamide-imide resin. The polyamide-imide resin includes a first constituent unit represented by Formula (1) and a second constituent unit represented by Formula (2). The percentage of the second constituent unit is in a range of 5 to 35% by mol.