An ultrasonic sensor for detecting an ultrasonic wave, which is output from an ultrasonic generator and reflected by an object to be detected, the ultrasonic sensor includes: an acoustic matching layer having a first surface and a second surface, the first surface which receives the ultrasonic wave, and the second surface which is opposite to the first surface; and an ultrasonic detection element including a vibration member. The vibration member is coupled with the second surface of the acoustic matching layer. The acoustic matching layer is repeatedly deformable in accordance with a standing wave, which is generated in the acoustic matching layer by the received ultrasonic wave. The vibration member resonates with the repeat deformation of the acoustic matching layer.