An ultrasonic sensor includes an element substrate having a first and a second surface at an opposite side of the first surface, including an opening section piercing through the element substrate in a Z direction from the first to second surface, a vibrating plate on the first surface of the element substrate to close the opening section, a plurality of vibration regions extending along an X direction orthogonal to the Z direction on the vibration plate in positions overlapping the opening section, and a plurality of piezoelectric elements to correspond to the plurality of vibration regions of the vibration plate. The opening section includes, on the first surface, a first and second side parallel to the X direction and a third and fourth side coupling end portions in the X direction of the first and second sides at an acute or obtuse angle to the first and the second side.