A coaxial microstripline transducer, having an inner conductor with a center conductor portion arranged in a recess portion of a resin case and a terminal portion which is integral with the center conductor portion and formed so as to lead to a lower surface of the resin case. An outer conductor has a first conductor portion arranged along at least a part of an inner peripheral surface of the recess portion and a second conductor portion which is integral with the first conductor portion and extended to the lower surface across an upper surface and across a pair of side surfaces opposed to each other of the resin case. The inner and outer conductors are fixed to the resin case. The outer conductor is preferably made of sheet metal material so as to enjoy low high-frequency losses. The first conductor portion advantageously is resilient and projects into the recess portion of the resin case to grip and engage a plug inserted into the transducer.