A high-frequency signal transmission line includes an element, a linear signal line provided at the element and including a first end and a second end, and at least one ground conductor provided at the element and extending along the signal line. The element includes stacked insulating layers. The ground conductor is positioned opposite to the signal line with the insulating layer positioned therebetween. The ground conductor is a contiguous conductor. The signal line, the ground conductor, and the element generate a characteristic impedance. The signal line includes a first section and a second section. The first section is an uninterrupted section generating a characteristic impedance greater than or equal to a first characteristic impedance at the first end and including the first end. The second section generates a characteristic impedance less than the first characteristic impedance and is adjacent to the first section. The second section is longer than the first section. The signal line is wider in the second section than in the first section.