To provide a coplanar line with a small attenuation caused by leakage of electromagnetic waves to a substrate in a millimeter wave band without forming any insulating film between a silicon monocrystalline substrate and a signal line, and to provide a method of manufacturing the coplanar line.

The coplanar line includes: a high resistive silicon substrate 22; a signal line 42 formed on the high resistive silicon substrate; and a pair of grounding conductors 44 formed in positions across the signal line on the high resistive silicon substrate. A concave portion 24 is formed in a main surface 22a side of the high resistive silicon substrate between the signal line and the grounding conductors.