An ultrasonic treatment apparatus includes a transmission member which has flexibility and to which an ultrasonic vibration is transmitted to perform ultrasonic treatment; a treatment portion which is provided at a distal end of the transmission member, and has a length approximately ½ of a wavelength of the ultrasonic vibration, a cross section area on a plane orthogonal to a transmission direction of the ultrasonic vibration, and a stiffness in which the cross section area is larger than a cross section area of the transmission member, a distal end of the treatment portion being located at an ultrasonic vibration antinode; and a grasping member which is provided to the treatment portion, opened or closed by an operation wire to grasp body tissue with the treatment portion, engaged with the treatment portion at the ultrasonic vibration node.