Provided is an ultrasonic endoscopic probe capable of obtaining an ultrasonic observation image having high spatial resolution. A part of a substantially tubular catheter is sealed with seal plates to provide a cavity housing: a motor including a motor casing, a rotor magnet, a bearing, and a rotating shaft; an ultrasonic transducer mounted to the rotating shaft; and a signal transmission means. The bearing includes an inner peripheral surface provided with a plurality of dynamic pressure generating grooves. An acoustic coupling fluid is sealed in the cavity and is allowed to penetrate a gap between the bearing and the rotating shaft at all times. When the ultrasonic transducer and the motor are rotated in the acoustic coupling fluid, the acoustic coupling fluid is suctioned in a preferable manner into the bearing gap having the dynamic pressure generating grooves for lubrication. Thus, a lack of an oil film on the bearing can be prevented, allowing for high accuracy rotation. Operational failure due to the development of foam in the acoustic coupling fluid can be prevented, enabling the acquisition of a high resolution ultrasonic observation image.