PURPOSE: To provide a filter circuit for the ultrasonic wave transducer in which the production of the undesired mode is avoided when an ultrasonic wave is generated.

CONSTITUTION: The filter circuit for the ultrasonic wave transducer excited by an exciting signal from a power supply section 10 provided with an ultrasonic wave transducer 40 represented by an equivalent circuit in which a capacitive component 41 is connected in parallel with a series circuit comprising an inductive component 42, a capacitive component 43 and a resistive component 44 has a matching circuit 20 matching with a signal from the power supply section 10 to the ultrasonic wave transducer and a filter circuit 60 comprising at least one component in each component of the ultrasonic wave transducer 40 and the matching circuit 20 and passing a component exciting only a predetermined ultrasonic wave from the signal from the power supply section 10.