One transmission line includes a first signal conductor which is placed on one surface of a substrate formed from a dielectric or semiconductor and which is formed so as to be curved toward a first rotational direction within the surface, and a second signal conductor which is formed so as to be curved toward a second rotational direction opposite to the first rotational direction and which is placed in the surface so as to be electrically connected in series to the first signal conductor, wherein a transmission-direction reversal portion in which a signal is transmitted along a direction reversed with respect to a signal transmission direction of the transmission line as a whole is formed so as to include at least part of the first signal conductor and part of the second signal conductor. Such a transmission line is capable of obtaining a suppression effect of unwanted radiation intensity.