Ultrasonic sensor and sensor attachment

A sensor attachment for use in attaching an ultrasonic sensor to a plate-like vehicle body member, the ultrasonic sensor being equipped with an ultrasonic microphone which is of a cylindrical shape and extends in an axial direction parallel to a center axis line, comprising:

• a cylinder which is configured to be disposed in a through-hole formed in the vehicle body member and surrounds the ultrasonic microphone in a vehicle-mounted state where the ultrasonic sensor is mounted in the vehicle body member;
• and
• a through-hole facing portion which is defined by a portion of the cylinder and extends in a radial direction perpendicular to the center axis line so as to face an inner surface of the through-hole in proximity thereto to be contactable with the inner surface in the vehicle-mounted state, the through-hole facing portion being configured to have a contact surface-decreasing structure which is configured to minimize an area of contact with the inner surface of the through- hole.