PURPOSE: To apply Doppler beam to a desired region, by such a simple structure that a Doppler mode measuring ultrasonic vibrator is arranged in an expansible and deformable bellows member.

CONSTITUTION: A water bag for an ultrasonic probe has an almost columnar shape and a volume variation absorbing means 5 for absorbing the volumetric change of a bellows like member 4 accompanied by the expansion, contraction and deformation thereof is mounted to the mount end part 1 with the ultrasonic transmitting and receiving end part 6b of the ultrasonic probe 6. A fixed two- split Doppler mode measuring ultrasonic vibrator 10 capable of taking CW Doppler is provided in the water bag 7. The B-mode measuring ultrasonic probe 6 and the Doppler mode measuring ultrasonic probe 10 are connected to an ultrasonic diagnostic apparatus main body 17 in a freely detachable manner by a connector.