The present invention is an electrical filter which includes coaxial resonators, for example, both-end open type 1/2 wave length TEM (transverse electro-magnetic mode) coaxial resonators, each having dielectric material, for example of titanium oxide group, filling the space between an inner conductor and an outer conductor of the resonator for reduction of size and weight of the resonator with optimum quality factor Q and temperature characteristics, while the predetermined number of these coaxial resonators are accommodated in one or more than two bores longitudinally formed in parallel relation to each other in a filter casing of conductive material for coupling the resonators to each other through capacitors.