Abstract: A band-pass filter for the microwave band consists of a dielectric substrate, a grounded conductor layer formed on the back surface of the substrate, input and output transmission line conductors formed on the front surface of the substrate, and a plurality of .lambda./2-length microstrip conductors formed between the input and output transmission line conductors such that they align in parallel over about .lambda./4 length. A through hole is formed through each .lambda./2-length microstrip conductor, the substrate and the grounded conductor layer at the center of the microstrip conductor. The .lambda./2-length microstrip conductor and the grounded conductor layer are electrically connected to each other through a conductive layer formed on the substrate wall of the through hole.