An ultrasonic sensor for emitting ultrasonic waves and for receiving the waves reflected from objects is mounted on a mounting member such as a bumper of an automotive vehicle. A through-hole for inserting a front portion of the ultrasonic sensor is formed in the bumper. The ultrasonic sensor is connected to an inner surface of the bumper using a fixing member so that a vibrating front surface of the ultrasonic sensor is exposed to the front side of the bumper. A front periphery of the through-hole which is rough due to machining burrs or the like is covered with a masking member formed separately from the mounting member. Thus, the ultrasonic sensor is easily mounted on a bumper without damaging its ornamental design.
