To provide a small-sized interdigital filter that has a small loss and a high no-load Q value.

In this interdigital filter where one-end short-circuited/other-end open quarter-wave resonators 141-146 are arranged interdigitally, in parallel between parallel ground conductor plates 10A, 10B, an input conductor 16A is placed at the outside of the 1st stage quarter-wave resonator 141 and an output conductor 16B is placed at the outside of the final stage 1/4 quarter-wave resonators 146 respectively in parallel, conductor rods 24 that short-circuit the parallel ground conductor plates 10A, 10B are respectively provided between the quarter-wave resonators 141 and 142, etc., between the quarter-wave resonators 145 and 146.