PURPOSE: To obtain a practical distribution constant type filter just with a planar circuit by arranging the parts of appropriate lengths of the open end parts of resonators set in parallel to each other on a dielectric substrate so that proper angles are obtained with each other.

CONSTITUTION: An earth conductor such as an earth, etc. is provided on the rear side of a plate-shaped dielectric substrate 1. While resonators 2 and 3 are set in parallel to each other on the upper surface side of the substrate 1. An end of each of resonators 2 and 3 is connected electrically to an earth conductor provided on the rear side of the substrate 1. Thus short circuit terminals 2a and 3a are obtained. At the same time, the appropriate length parts of resonators 2b and 3b adjacent to each other are arranged so that said length parts form a proper angle with each other or open end parts 2b and 3b are set so as to secure a space between them. Furthermore the parts 2b and 3b of the resonators 2 and 3 are connected to an input terminal 5a and an output terminal 5b respectively via a coupling capacitor 4 for capacitive coupling.