To obtain the ladder filter in which disturbance in the filter characteristic is less.
The ladder filter 10 includes a support board 12 made of an insulation material. Support members 22, 24, 26, 28, 30, 32, 34, 36 are fitted to a land formed to pattern electrodes 14, 16, 18, 20 on the support board 12. Piezoelectric resonators 50a, 50b, 50c, 50d are fitted on the support members 22-36 to form the filter connected to be a ladder. The piezoelectric resonators 50a, 50b, 50c, 50d have a board laminating the piezoelectric layer and the electrodes and the electrode s are connected to external electrodes 62, 64 formed to one side face of the board. Let a width of the piezoelectric resonators 50a, 50b, 50c, 50d, be (w) and its thickness be (t) and number of laminators be (n), then a relation of 1≤log10(n2wt)≤3 is established.
UNAMI TOSHIHIKO
TAKESHIMA TETSUO
