An ultrasonic endoscope (12, 12a, 12b, 12c, 12d, 12) comprising a plurality of ultrasonic vibrators at a distal end part of the ultrasonic endoscope, comprising: an ultrasonic vibrator unit provided at the distal end part, the ultrasonic vibrator unit being composed of at least an ultrasonic vibrator array and a first thermally conductive member, the ultrasonic vibrator array having the plurality of ultrasonic vibrators that are arranged in a cylindrical form, the first thermally conductive member being disposed thermally in contact with the ultrasonic vibrator array; a plurality of cables that are electrically connected to the ultrasonic vibrator array; and an electrically conductive structural body that is disposed to extend from a distal end side toward a proximal end side of the ultrasonic endoscope (12, 12a, 12b, 12c, 12d, 12), wherein the ultrasonic vibrator unit and the electrically conductive structural body are connected to each other via an electrically insulating second thermally conductive member (102,106,108,108a,108b), and wherein the first thermally conductive member is a metal ring composed of six integral and axially aligned cylindrical portions, the six cylindrical portions comprising, disposed axially in succession, a distal first cylindrical portion having a first outer diameter, a second cylindrical portion having a second outer diameter greater than the first outer diameter, a third cylindrical portion having a third outer diameter smaller than the first outer diameter, a fourth cylindrical portion having a fourth outer diameter greater than the second outer diameter, a fifth cylindrical portion having a fifth outer diameter equal to the fourth outer diameter, and a proximal sixth cylindrical portion having a sixth outer diameter greater than the fifth outer diameter; wherein the first to fourth cylindrical portions have a first inner diameter, the fifth cylindrical portion has a second inner diameter greater than the first inner diameter and the sixth cylindrical portion has a third inner diameter greater than the second inner diameter, wherein the plurality of cables extend through a cutout in the third and fourth cylindrical portions and wherein the sixth cylindrical portion is configured to receive a screw passing therethrough for attachment of the first thermally conductive member to the structural body; and wherein a backing material layer of the ultrasonic vibrator array having a cylindrical inner surface is disposed on the outer peripheral surface of the first thermally conductive member so as to extend, from the distal end of the third cylindrical portion, axially partially over the cylindrical outer peripheral surface of the third cylindrical portion. an ultrasonic vibrator unit provided at the distal end part, the ultrasonic vibrator unit being composed of at least an ultrasonic vibrator array and a first thermally conductive member, the ultrasonic vibrator array having the plurality of ultrasonic vibrators that are arranged in a cylindrical form, the first thermally conductive member being disposed thermally in contact with the ultrasonic vibrator array; the ultrasonic vibrator unit being composed of at least an ultrasonic vibrator array and a first thermally conductive member, the ultrasonic vibrator array having the plurality of ultrasonic vibrators that are arranged in a cylindrical form, the first thermally conductive member being disposed thermally in contact with the ultrasonic vibrator array; a plurality of cables that are electrically connected to the ultrasonic vibrator array; and an electrically conductive structural body that is disposed to extend from a distal end side toward a proximal end side of the ultrasonic endoscope (12, 12a, 12b, 12c, 12d, 12), wherein the ultrasonic vibrator unit and the electrically conductive structural body are connected to each other via an electrically insulating second thermally conductive member (102,106,108,108a,108b), and wherein the first thermally conductive member is a metal ring composed of six integral and axially aligned cylindrical portions, the six cylindrical portions comprising, disposed axially in succession, a distal first cylindrical portion having a first outer diameter, a second cylindrical portion having a second outer diameter greater than the first outer diameter, a third cylindrical portion having a third outer diameter smaller than the first outer diameter, a fourth cylindrical portion having a fourth outer diameter greater than the second outer diameter, a fifth cylindrical portion having a fifth outer diameter equal to the fourth outer diameter, and a proximal sixth cylindrical portion having a sixth outer diameter greater than the fifth outer diameter; wherein the first to fourth cylindrical portions have a first inner diameter, the fifth cylindrical portion has a second inner diameter greater than the first inner diameter and the sixth cylindrical portion has a third inner diameter greater than the second inner diameter, wherein the plurality of cables extend through a cutout in the third and fourth cylindrical portions and wherein the sixth cylindrical portion is configured to receive a screw passing therethrough for attachment of the first thermally conductive member to the structural body; and wherein a backing material layer of the ultrasonic vibrator array having a cylindrical inner surface is disposed on the outer peripheral surface of the first thermally conductive member so as to extend, from the distal end of the third cylindrical portion, axially partially over the cylindrical outer peripheral surface of the third cylindrical portion.