A grasping treatment device comprising: a probe extending along a longitudinal axis and configured to transmit ultrasonic vibrations from a proximal end to a distal end along the longitudinal axis; a sheath through which the probe is inserted so that the probe protrudes toward a distal direction; a jaw which is attached to a distal portion of the sheath rotatably around a rotation axis perpendicular to the longitudinal axis, and which is configured to open/close relative to a distal portion of the probe in open/close directions (A1, A2) perpendicular to the longitudinal axis and perpendicular to the rotation axis, characterized in that a position of the rotation axis of the jaw coinciding with a node position of the ultrasonic vibrations in directions parallel to the longitudinal axis; and further comprising: a support member which is provided between the probe and the sheath, and which is configured to prevent contact between the probe and the sheath, the sheath being configured to support the probe via the support member, wherein the support member includes a most-distal support member which is located on the most distal direction side, a position of the most-distal support member coinciding with the position of the rotation axis of the jaw in the directions parallel to the longitudinal axis, and a coupling portion (62A, 62B, 63A, 63B, 92A, 92B, 93A, 93B) which couples the jaw with the sheath at a position where the sheath supports the probe via the most-distal support member in the directions parallel to the longitudinal axis so that the rotation axis of the jaw passes through the probe at the position where the sheath supports the probe via the most-distal support member in the directions parallel to the longitudinal axis, the sheath being configured to support the probe via the support member such that a deflection of the probe at the position of the most-distal support member is prevented. a probe extending along a longitudinal axis and configured to transmit ultrasonic vibrations from a proximal end to a distal end along the longitudinal axis; a sheath through which the probe is inserted so that the probe protrudes toward a distal direction; a jaw which is attached to a distal portion of the sheath rotatably around a rotation axis perpendicular to the longitudinal axis, and which is configured to open/close relative to a distal portion of the probe in open/close directions (A1, A2) perpendicular to the longitudinal axis and perpendicular to the rotation axis, characterized in that a position of the rotation axis of the jaw coinciding with a node position of the ultrasonic vibrations in directions parallel to the longitudinal axis; and further comprising: a support member which is provided between the probe and the sheath, and which is configured to prevent contact between the probe and the sheath, the sheath being configured to support the probe via the support member, wherein the support member includes a most-distal support member which is located on the most distal direction side, a position of the most-distal support member coinciding with the position of the rotation axis of the jaw in the directions parallel to the longitudinal axis, and a coupling portion (62A, 62B, 63A, 63B, 92A, 92B, 93A, 93B) which couples the jaw with the sheath at a position where the sheath supports the probe via the most-distal support member in the directions parallel to the longitudinal axis so that the rotation axis of the jaw passes through the probe at the position where the sheath supports the probe via the most-distal support member in the directions parallel to the longitudinal axis, the sheath being configured to support the probe via the support member such that a deflection of the probe at the position of the most-distal support member is prevented. a support member which is provided between the probe and the sheath, and which is configured to prevent contact between the probe and the sheath, the sheath being configured to support the probe via the support member, wherein the support member includes a most-distal support member which is located on the most distal direction side, a position of the most-distal support member coinciding with the position of the rotation axis of the jaw in the directions parallel to the longitudinal axis, and a coupling portion (62A, 62B, 63A, 63B, 92A, 92B, 93A, 93B) which couples the jaw with the sheath at a position where the sheath supports the probe via the most-distal support member in the directions parallel to the longitudinal axis so that the rotation axis of the jaw passes through the probe at the position where the sheath supports the probe via the most-distal support member in the directions parallel to the longitudinal axis, the sheath being configured to support the probe via the support member such that a deflection of the probe at the position of the most-distal support member is prevented.