The first transmission line has a width perpendicular to a transmission direction. The first electrode has a width not exceeding the width. The first electrode is opposed to the first transmission line. The ground layer has a positional relationship with each portion of the first transmission line. The ground layer is next to the first transmission line on at least one side consisting of a first side along a thickness direction of the mounting substrate, and a second side and a third side with the first transmission line interposed therebetween. The first transmission line is bonded to the first electrode and has the width equivalently, at least, at a portion of the first transmission line. The portion equivalently has the positional relationship with the ground layer. The portion is next to the ground layer in an equivalent shape along the transmission direction.