To solve the problems of a conventional low pass filter being difficult to widen an attenuation frequency range for the conventional low pass filter consisting of microstrip lines, having unable to obtain sufficient attenuation especially at a high frequency, multi-stage cascade connection of the low pass filters for the purpose of extending the attenuation frequency range increases the entire size and the loss in the pass band and unwanted waves cause multiple reflections in a microwave device, resulting in deteriorating the amplitude frequency characteristics.

One or more resistive films are formed to a prescribed part, especially around an inductive impedance part of a low pass filter pattern. Through this configuration, the attenuation area of the low pass filter is widened and the resistance film attenuates reflected unwanted waves, to suppress multiple reflections of the unwanted waves.