ultrasound unit 30 comprises a plurality of elements 60 including N cells 9 and an upper electrode 16A constituting the lower electrode 11A and the membrane 18 are opposed to each other via a cavity 13, the element 60 There, N 1 and the number of the first cell 9A, low high transmission sensitivity reception sensitivity than that of the first cell 9A N 2 number (however, N 1 N 2 , with the N 1 + N 2 = N second cell of 9B).
