Disclosed is a method of manufacturing a BPF (bandpass filter) for GHz bands of the structure that an input signal line (2) and an output signal line (3) run with a small gap on one surface of a sheet (1) made by dispersing soft magnetic metal powder in a sheet-formed polymer matrix, an internal line (6) bridges on the signal lines, and a GND line (4) runs on the reverse surface of the sheet. The method comprises inserting an intermediate product made by disposing on both the sides of an insulating film (5) the above-mentioned input signal line (2), output signal line (3) and internal line (6), on one side of the cavity of a mold for injection, and inserting a metal piece for the GND line (4) on the other side of the cavity; and injecting a polymer compound to obtain a molded article.