To provide an ultrasonic leak detector, in which abnormal sounds larger than an ultrasonic sound radiated by leakage is narrowed down, so as to be output to an output part.

The ultrasonic leak detector 1 is provided with ultrasonic microphones 6, 7, 8 which have directivity. The detector 1 is provided with a signal processing circuit 11, which processes electrical signals detected by the microphones 6, 7, 8. The detector 1 is provided with a headphone 14, which outputs the signals processed by the processing circuit 11. The processing circuit 11 is provided with an automatic volume control part 25, which narrows down a signal, when the signal at a set value or more is input and which outputs the signal to the headphone 14. The control part 25 narrows down the signal, when the signal at the set value or more is input, and it outputs the signal to the output part. As a result, the abnormal sound which is larger than the ultrasonic sound radiated by the leak is not output to the headphone 14 as is.