An ultrasonic sensor attached to a certain object, includes an ultrasonic detecting element, an acoustic matching member, and a reflection limiting member. The ultrasonic detecting element detects an ultrasonic wave. The acoustic matching member has a receiving surface that is adapted on a side of the certain object to face toward the detected body. The reflection limiting member is disposed to a side portion of the acoustic matching member between the receiving surface and an opposing surface of the acoustic matching member. The reflection limiting member limits the ultrasonic wave, which transmits inside the acoustic matching member, from being reflected by the side portion.