PURPOSE: To widen the width of a double harmonic wave directing angle by providing a step on the array of the radiation surface of an incorporated element.

CONSTITUTION: X-Y indicates an element array reference plane, the normal direction thereof is a Z axis and the center of the element array is disposed along the straight line X-Y. The number of the array elements is five, the diameter D of the radiation surface of the element is entirely 30 mm, the quantities of the steps from the element array reference plane of the respective element radiation surfaces from the element array reference plane (X-Y), are Z1=9 mm, Z2=2 mm, Z3=0 mm, Z4=2 mm, Z5=9 mm, and intervals between the elements are d1=29 mm, d2=14.5 mm, d3=0 mm, d4=14.5 mm, d5=29 mm. A sound wave transmitter/receiver has the same constitution and a basic wave has 20 kHz, and the double harmonic wave has 100 kHz. Thereby, the survey range of the double harmonic wave can be remarkably enlarged by hardly changing the prescribed survey range in the basic wave in a multifrequency type sound wave transmitter-receiver.