An ultrasonic probe transmits vibration along longitudinal axis from the proximal toward the distal end, including: first area including proximal and distal end portions, a center axis parallel to the longitudinal axis, the first area having a vibration antinode position at the distal end, wherein maximum distance from the center axis to an outer peripheral surface in radial direction orthogonal to the center axis is a first distance； a treatment section located on a distal end side's barycenter position displaced from the center axis； a second area located between the first area and treatment section continuous with the distal end of the first area and gravity center axis parallel to the center axis to pass through the barycenter, wherein maximum distance from the center axis to the outer surface in the radial direction orthogonal to the center axis is a second distance equal to or shorter than the first distance.
