A connection mechanism for an ultrasonic-vibration generating/transmitting unit, the connection mechanism comprising: a first member which has an end face at one end portion and which is provided with a first connection portion at the one end portion and which is configured to transmit ultrasonic vibration; a second member which is provided with a diametrically protruding held portion at one end portion, which is configured to transmit the ultrasonic vibration, the length of the held portion in the circumferential direction of the one end portion being a prescribed length; and a cylindrical third member which has one end portion and another end portion and which connects the first member and the second member to each other, the third member comprising a protrusion portion which protrudes inward from an inner circumferential surface at the one end portion of the third member, an opening portion (D2, 307) which is provided at the one end portion of the third member, and the opening portion (D2, 307) being longer than the prescribed length of the second member so that the held portion is able to be inserted into or removed from the opening portion (D2, 307), and a second connection portion which is provided on the inner circumferential surface of the other end portion of the third member and which is connected to the first connection portion characterized in that the protrusion portion forms a first space portion between the end face of the first member and the protrusion portion while the first member is inserted from the other end portion of the third member, and the first connection portion is movable relative to the third member in the axial direction of the third member to adjust the length of the first space portion formed between the end face of the first member and the protrusion portion, wherein, with the held portion of the second member inserted from the opening portion (D2, 307) of the third member, and disposed in the first space portion between the protrusion portion and the end face of the first member, the third member moves the protrusion portion relative to the first member so that the protrusion portion presses the held portion against the end face of the first member, and the third member thereby holds the held portion between the end face and the protrusion portion. a first member which has an end face at one end portion and which is provided with a first connection portion at the one end portion and which is configured to transmit ultrasonic vibration; a second member which is provided with a diametrically protruding held portion at one end portion, which is configured to transmit the ultrasonic vibration, the length of the held portion in the circumferential direction of the one end portion being a prescribed length; and a cylindrical third member which has one end portion and another end portion and which connects the first member and the second member to each other, the third member comprising a protrusion portion which protrudes inward from an inner circumferential surface at the one end portion of the third member, an opening portion (D2, 307) which is provided at the one end portion of the third member, and the opening portion (D2, 307) being longer than the prescribed length of the second member so that the held portion is able to be inserted into or removed from the opening portion (D2, 307), and a second connection portion which is provided on the inner circumferential surface of the other end portion of the third member and which is connected to the first connection portion characterized in that the protrusion portion forms a first space portion between the end face of the first member and the protrusion portion while the first member is inserted from the other end portion of the third member,