PURPOSE: To vary the directivity of a radiation ultrasonic wave and to make a titled transmitter cope with a lot of use purposes by varying the position relation of a transmitting microphone and a horn provided in its front.

CONSTITUTION: A transmitting circuit 1, a transmitting microphone 2 and a horn are provided in a transmitter case 5, and the horn 3 can be moved back and forth as indicated with an arrow M by a knob 4. When the horn 3 is made to come in front of the microphone 2, directivity 6 of an ultrasonic wave radiated from a transmitter becomes sharp, and when the microphone 2 is made to go into a horn part of the horn 3, the directivity of the ultrasonic wave becomes wide. In this way, it is possible to operate only a specified one from plural objects to be operated, or to operate simultaneously all of the plural objects to be operated, by one transmitter.