An ultrasonic probe, comprising: a probe main body portion which extends along a longitudinal axis, and configured to transmit an ultrasonic vibration from a proximal side toward a distal side; a treatment section provided in a distal portion of the probe main body portion; an insulation layer portion which coats an outer surface of the probe main body portion from the treatment section toward the proximal side; a first electrode portion (38A;38) provided on an outer surface of the insulation layer portion so that at least part of the first electrode portion (38A;38) is exposed to an outside in the treatment section, the first electrode portion (38A;38) having conductivity for conveying a high-frequency electric power, and being configured to apply the high-frequency electric power; a second electrode portion (38B;45) provided so that at least part of the second electrode portion (38B;45) is exposed to the outside in the treatment section, the second electrode portion (38B;45) being configured to function as an electrode different from the first electrode portion (38A;38), being electrically insulated from the first electrode portion (38A;38) by the insulation layer portion, and being configured to vibrate integrally with the probe main body portion, the insulation layer portion, and the first electrode portion (38A;38) when the probe main body portion transmits the ultrasonic vibration; and a first insulation coating portion (42A;42) formed from the treatment section toward the proximal side, and made of an electrically insulating material, the first insulation coating portion (42A;42) covering the first electrode portion (38A;38) other than an exposed part to the outside in the treatment section, wherein the probe main body portion is configured to vibrate at a predetermined resonance frequency by transmitting the ultrasonic vibration, characterized in that: when a position where a dimension from a distal end of the probe main body portion toward the proximal side is a 1/4 wavelength of the ultrasonic vibration at the predetermined resonance frequency is a reference position, the insulation layer portion extends to a position on the proximal side with respect to the reference position, and a proximal end of the first electrode portion (38A;38) is located on the distal side with respect to a proximal end of the insulation layer portion. a probe main body portion which extends along a longitudinal axis, and configured to transmit an ultrasonic vibration from a proximal side toward a distal side; a treatment section provided in a distal portion of the probe main body portion; an insulation layer portion which coats an outer surface of the probe main body portion from the treatment section toward the proximal side; a first electrode portion (38A;38) provided on an outer surface of the insulation layer portion so that at least part of the first electrode portion (38A;38) is exposed to an outside in the treatment section, the first electrode portion (38A;38) having conductivity for conveying a high-frequency electric power, and being configured to apply the high-frequency electric power; a second electrode portion (38B;45) provided so that at least part of the second electrode portion (38B;45) is exposed to the outside in the treatment section, the second electrode portion (38B;45) being configured to function as an electrode different from the first electrode portion (38A;38), being electrically insulated from the first electrode portion (38A;38) by the insulation layer portion, and being configured to vibrate integrally with the probe main body portion, the insulation layer portion, and the first electrode portion (38A;38) when the probe main body portion transmits the ultrasonic vibration; and a first insulation coating portion (42A;42) formed from the treatment section toward the proximal side, and made of an electrically insulating material, the first insulation coating portion (42A;42) covering the first electrode portion (38A;38) other than an exposed part to the outside in the treatment section, wherein the probe main body portion is configured to vibrate at a predetermined resonance frequency by transmitting the ultrasonic vibration, when a position where a dimension from a distal end of the probe main body portion toward the proximal side is a 1/4 wavelength of the ultrasonic vibration at the predetermined resonance frequency is a reference position, the insulation layer portion extends to a position on the proximal side with respect to the reference position, and a proximal end of the first electrode portion (38A;38) is located on the distal side with respect to a proximal end of the insulation layer portion.