In an ultrasonic probe, a curved portion gravity center of a probe curved portion located on a first perpendicular direction side with respect to a longitudinal axis. A boundary position between a probe relay portion and a probe main body portion is located on a distal side with respect to a reference antinode position which is located most distally among antinode positions of a longitudinal vibration located on a proximal direction side with respect to the probe curved portion. By a cross-section changing portion located at the boundary position, a cross section gravity center in a cross section of the probe relay portion perpendicular to the longitudinal axis is away from the longitudinal axis toward a second perpendicular direction opposite to the first perpendicular direction.