An ultrasonic testing apparatus includes an ultrasonic probe disposed under an end portion of a pipe laid in the horizontal direction to face the pipe end portion. The probe transmits ultrasonic waves to the end portion of the pipe and receives the ultrasonic waves therefrom. A probe holder housing the probe includes a coupling medium reserver part which surrounds a space between the probe and the end portion of the pipe to contain a coupling medium W. The coupling medium reserver part includes a part body 21 into which the coupling medium is supplied; an annular bellows part, which is attached to the upper side of the part body to internally communicate with the part body, and an annular spacer 23 attached to the upper side of the bellows part, the upper surface of the annular spacer being a flat horizontal surface.