A fish school finding device capable of efficiency acquiring information is realized since the measurement area is automatically set. The device includes: an individual fish detecting module 41 configured to detect an individual fish from echo information obtained from ultrasonic waves transmitted in a depth direction at predetermined time intervals; an individual fish number calculating module 42 configured to calculate a number of the individual fish for each of a plurality of two-dimensionally arrayed sections consisting of the depth direction and a time axis direction; a reference section detecting module 43 configured to detect a reference section based on the number of the individual fish; and a measurement area setting module 44 configured to set a measurement area based on the reference section.
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