A multilayer substrate includes a laminate, first and second signal lines, first and second ground conductors, and interlayer connection conductors. The first and second signal lines extend along a transmission direction and include parallel extending portions that extend in parallel or substantially in parallel with each other. The first and second ground conductors sandwich the first and second signal lines in a laminating direction. The first and second ground conductors respectively include a first opening and a third opening between the signal lines when viewed from the laminating direction, and respectively include second openings and fourth openings disposed outside in a width direction orthogonal or substantially orthogonal to the transmission direction in the parallel extending portions when viewed from the laminating direction. The interlayer connection conductors are disposed in the transmission direction and at least between the signal lines.