The objective of this study was to design and develop a broadband ultrasonic transducer that has both wide bandwidth and high sensitivity to measure broadband echoes related to identifying fish species. A broadband ultrasonic transducer providing a nearly flat transmitting response band of 40.2-75.5 kHz with a -12 dB bandwidth of 35.3 kHz was achieved by integrating 12 tonpilz transducer elements operating at different resonance frequencies. The average transmitting voltage response, receiving sensitivity, and figure of merit values in this frequency band were 168.4 dB (re $1{mu}Pa/V$ at 1 m), -196.8 dB (re $1V/{mu}Pa$), and -28.4 dB, respectively. The results suggest that bandwidth and sensitivity can be widened and improved by adjusting the array pattern and the structure of tonpilz transducer elements.