PURPOSE: To make it possible to keep an ultrasonic acoustic coupler fixed to an ultrasonic probe regardless of whether an ultrasonic propagating medium is used or not.

CONSTITUTION: This ultrasonic acoustic coupler has a mounting member 2 mountable to the ultrasonic probe 1 and a holding arm 6 having an insertion rod 5 inserted into a holding 4 bored in the ultrasonic propagating medium 3 having an approximately rectangular parallelepiped shape. This holding arm 6 is constituted to have the insertion rod 5 existing in the aperture on the rear surface of the mounting member 2 and to be mounted freely turnably on the wall surface of the mounting member 2 in such a manner that the arm is movable from a holding position where the ultrasonic propagating medium 3 is held to a retreat position along the side wall of the mounting member 2.