An ultrasonic transducer (1) includes "m" first ultrasonic elements (8a) including first diaphragms (51a), and "n" second ultrasonic elements (8b) including second diaphragms (51b). "m" represents a number of the first ultrasonic elements (8a) and is an integer of 1 or more. Each of the first diaphragms (51a) has a first area. "n" second ultrasonic elements (8b) includes second diaphragms (51b). Each of the "n" second diaphragms (51b) has a second area being smaller than the first area. "n" represents a number of the second ultrasonic elements (8b) and is an integer larger than "m". The "m" first ultrasonic elements (8a) are electrically connected in series in a case where "m" is an integer of 2 or more. The "n" second ultrasonic elements (8b) are electrically connected in series. B/A is within a range of 0.9 to 1.1, when a total sum of the first areas is "A" and a total sum of the second areas is "B".
