A multilayer substrate includes a differential line including first and second line conductors provided on or in a laminated body including base material layers. The differential line includes line portions and a connecting portion that connects the line portions. The connecting portion includes first parallel conductors extending in parallel or substantially in parallel with each other, first interlayer connecting conductors that connect the first parallel conductors in parallel, and connect the first line conductor to the first parallel conductors, second parallel conductors extending in parallel or substantially in parallel with each other, and second interlayer connecting conductors that connect the second parallel conductors in parallel, and connect the second line conductor to the second parallel conductors. The first parallel conductors cross the second parallel conductors as viewed in a laminating direction of the base material layers.