An ultrasonic probe has an organism contact portion that is shaped for use along a comparatively large curvature and can easily be used while closely contacting an organism. The probe includes a first cylinder pulley secured to a probe casing, an arm secured to a motor spindle extending through the first pulley, and a second cylinder pulley rotatably arranged on the opposite side and coupled to the first pulley by a wire. The second pulley is equipped with a slider shaft that is arranged to be extendable by a slider bearing. The slider shaft is equipped with a roller contacting a guide rail of the casing. An ultrasonic element is attached to the distal end of the slider shaft to provide the telescopic structure for the slider shaft. In this manner, the size of a scanning mechanism, for oscillating the ultrasonic element along a large curvature, is reduced.