A width of each of a first signal terminal and a reference potential terminal formed in a first connection region of a core insulating layer constituting a flexible substrate is larger than a width of each of a first backside signal terminal and a backside reference potential terminal formed in a second connection region of the core insulating layer. In addition, a first separation distance between the first signal terminal and the reference potential terminal arranged adjacent to the first signal terminal is smaller than a second separation distance between the first backside signal terminal and the backside reference potential terminal arranged adjacent to the first backside signal terminal. An insulating film formed on a first surface of the core insulating layer at a position overlapping each of the first connection region and the second connection region covers the first connection region such that the second connection region is exposed.