A semi-coaxial cavity resonator filter including a plurality of semi-axial cavity resonators, as constructed units, each of which has an adjustable device in which dielectric substrates having a specific dielectric constant of more than 1 are disposed in the gap between the inside wall of a tube-shaped outer conductor and the open end of an inner conductor provided on the inside wall of the outer conductor, and the electrostatic capacitance of the spaces interposed by the dielectric substrates is changed without steps by varying the area of the electrodes on the dielectric substrate. The filter is made by making an individual and predetermined frequency adjustment on the plurality of the semi-axial cavity resonators and then cascade-connecting those resonators in one block through shielding plates having a coupling iris so as to obtain desired filtering characteristics as a bandpass filter.