A microwave circuit includes a concentric-circle-like prominence (7) formed on a contact surface which is on the side of a metal body (3) serving as an external conductor of a coaxial line and which connects a conductor strip (1) of an MSL formed on a dielectric substrate (2) to an internal conductor of the coaxial line through a through-hole (9) extending from a ground plane (11) of the MSL through the dielectric substrate (2). The construction involves no mismatched portion and can prevent a loss and deterioration in VSWR in the coaxial-line/MSL conversion section, thereby making it possible to obtain satisfactory characteristics.