Ultrasonic endoscope including treatment-tool erecting base for erecting treatment tool that is led out from opening formed in distal end rigid portion of endoscope insertion section

An ultrasonic endoscope comprising:

• a distal end rigid portion that is located at a distal end of an endoscope insertion section;
• an ultrasonic transducer that is disposed in the distal end rigid portion;
• a treatment tool lead-out portion that is disposed on a proximal end side of the ultrasonic transducer and that comprises
• an erecting base housing portion that has an opening whose opening direction is toward one side in a first direction that is perpendicular to an axial direction of the distal end rigid portion or whose opening direction is a direction that has a component toward the one side in the first direction and a component toward a distal end side in the axial direction of the distal end rigid portion,
• an opening forming surface in which the opening is formed and that has a normal component in the opening direction,
• a treatment tool lead-out port that communicates with an inside of the erecting base housing portion and from which a treatment tool is led out, and
• a treatment-tool erecting base that is disposed in the inside of the erecting base housing portion and that changes a lead-out direction of the treatment tool led out from the treatment tool lead-out port;
• and
• an observation window that is disposed on a proximal end side of the opening forming surface and that is disposed in an observation means forming surface that has a normal component toward the distal end side in the axial direction of the distal end rigid portion,
• wherein, when a position of an end portion of the opening that is furthest toward the one side in the first direction is defined as a one-side opening position, a position of the observation window in the first direction is located on the one side in the first direction relative to the one-side opening position, and
• wherein the observation window is disposed offset from the treatment-tool erecting base in a second direction that is perpendicular to the axial direction of the distal end rigid portion and perpendicular to the first direction.