A ladder-type electric filter apparatus having at least one electric filter unit wherein each electric filter unit includes a casing into which piezoelectric resonator elements and an input, output and earth terminal plates are mounted, one or two of said terminal plates are integrally formed together with the casing, the connecting leg(s) of said terminal plate(s) integrally formed together with the casing are protruded through the wall portion opposite to the opening of the casing, and the remaining terminal plate(s) have a connecting leg(s) protruded from the opening side, all of the connecting legs being connected to a printed circuit board.