An ultrasonic sensor comprising: a case having a bottom portion; and a piezoelectric element (50A, 50B, 50C, 50D, 50E, 50F, 50G, 50H) bonded to an inner surface of the bottom portion and configured to undergo bending vibration together with the bottom portion, the piezoelectric element including a piezoelectric layer including a transmission region, a reception region, and an isolation region, a common electrode having a shape extending across both the transmission region and the reception region, a transmission electrode facing the common electrode with the transmission region being interposed therebetween, and a reception electrode facing the common electrode with the reception region being interposed therebetween, the transmission region and the reception region being formed at positions adjacent to each other with the isolation region being interposed therebetween in a surface direction of the inner surface of the bottom portion, characterised by the transmission region including one first constituent piezoelectric layer or a plurality of first constituent piezoelectric layers (N1, N2, N3, N4, N5, N6, N7, N8) layered in a direction of being further away from the bottom portion, the plurality of first constituent piezoelectric layers being electrically connected in parallel, the reception region including one second constituent piezoelectric layer or a plurality of second constituent piezoelectric layers layered in the direction of being further away from the bottom portion, the plurality of second constituent piezoelectric layers being electrically connected in parallel, the number of the one or the plurality of first constituent piezoelectric layers included in the transmission region being different from the number of the one or the plurality of second constituent piezoelectric layers included in the reception region, one or a plurality of float electrodes (70, 71, 72, 73, 74, 75, 76, 77) being provided in one of the transmission region and the reception region, the one of the transmission region and the reception region having a smaller number of layers. a case having a bottom portion; and a piezoelectric element (50A, 50B, 50C, 50D, 50E, 50F, 50G, 50H) bonded to an inner surface of the bottom portion and configured to undergo bending vibration together with the bottom portion, the piezoelectric element including a piezoelectric layer including a transmission region, a reception region, and an isolation region, a common electrode having a shape extending across both the transmission region and the reception region, a transmission electrode facing the common electrode with the transmission region being interposed therebetween, and a reception electrode facing the common electrode with the reception region being interposed therebetween, a piezoelectric layer including a transmission region, a reception region, and an isolation region, a common electrode having a shape extending across both the transmission region and the reception region, a transmission electrode facing the common electrode with the transmission region being interposed therebetween, and a reception electrode facing the common electrode with the reception region being interposed therebetween, the transmission region and the reception region being formed at positions adjacent to each other with the isolation region being interposed therebetween in a surface direction of the inner surface of the bottom portion, characterised by the transmission region including one first constituent piezoelectric layer or a plurality of first constituent piezoelectric layers (N1, N2, N3, N4, N5, N6, N7, N8) layered in a direction of being further away from the bottom portion, the plurality of first constituent piezoelectric layers being electrically connected in parallel, the reception region including one second constituent piezoelectric layer or a plurality of second constituent piezoelectric layers layered in the direction of being further away from the bottom portion, the plurality of second constituent piezoelectric layers being electrically connected in parallel, the number of the one or the plurality of first constituent piezoelectric layers included in the transmission region being different from the number of the one or the plurality of second constituent piezoelectric layers included in the reception region, one or a plurality of float electrodes (70, 71, 72, 73, 74, 75, 76, 77) being provided in one of the transmission region and the reception region, the one of the transmission region and the reception region having a smaller number of layers.