PURPOSE: To reduce the irregularity of insertion loss and increase a band by dividing output transducers into several groups.

CONSTITUTION: Output transducers 21 to 2N are divided into m-number groups. Now, if N=8 and m=2 and 2≤m≤N/2 are ture, they can be divided into a group of transducers 21 to 24 and a group of transducers 25 to 28, and a more succeeding- stage transducer receives a smaller output voltage amplitude. Therefore, when load resistances having the relation of R1<R2 are connected to the preceding-stage and the succeeing-stage transducer groups, the irregularity of the output amplitude between transducers is reduced. Meanwhile, it is sufficient for diode switch circuits 31 to 3N provided between transducer groups and resistances R1 and R2 if they are constituted by pin diodes D1 and D2, resistances RA and RB and capacitor C1, and the circuit becomes simple. Thus, since output transducers are divided into m- number groups and matching coils L1 and L2 and load resistances R1 and R2 are provided in each group, capacity C is reduced and a band is extended