A vibration transmitting unit comprising: an extending portion which extends along a longitudinal axis, and which is capable of transmitting ultrasonic vibration from a proximal side to a distal side; a first component which is provided in the extending portion, and which has a first cross-sectional area in a cross-section perpendicular to the longitudinal axis; a second component which is provided on the distal side with respect to the first component in the extending portion, and which has a second cross-sectional area, which is larger than the first cross-sectional area, in a cross-section perpendicular to the longitudinal axis; and a third component which is provided between the first component and the second component in the extending portion, and which has a third cross-sectional area, which is larger than the first cross-sectional area and is smaller than the second cross-sectional area, in a cross-section perpendicular to the longitudinal axis, a standard vibration anti-node, which is one of vibration anti-nodes (A1, A2, A3, A4), being positioned at the third component by the ultrasonic vibration causing the extending portion to vibrate at a frequency in a predetermined frequency range (Δf), defined as the range between a minimum resonance frequency and a maximum resonance frequency of the vibration transmitting unit, the third component having a region in which the third cross-sectional area is constant in a direction parallel to the longitudinal axis, wherein the extending portion includes a cross-sectional reduction portion which is provided on the proximal side with respect to the first component, and which reduces a cross-sectional area perpendicular to the longitudinal axis towards the distal side to the first cross-sectional area of the first component, and wherein, in a state where the extending portion vibrates at a frequency in the predetermined frequency range (Δf), all of the vibration anti-nodes (A1, A2, A3, A4) are positioned away from the cross-sectional reduction portion in the direction parallel to the longitudinal axis, characterized in that a standard fluctuation width (ΔY), which is a fluctuation width of the standard vibration anti-node in the direction parallel to the longitudinal axis when a resonance frequency is changed in the predetermined frequency range (Δf), is equal to or less than an extending dimension of the third component in the direction parallel to the longitudinal axis. an extending portion which extends along a longitudinal axis, and which is capable of transmitting ultrasonic vibration from a proximal side to a distal side; a first component which is provided in the extending portion, and which has a first cross-sectional area in a cross-section perpendicular to the longitudinal axis; a second component which is provided on the distal side with respect to the first component in the extending portion, and which has a second cross-sectional area, which is larger than the first cross-sectional area, in a cross-section perpendicular to the longitudinal axis; and a third component which is provided between the first component and the second component in the extending portion, and which has a third cross-sectional area, which is larger than the first cross-sectional area and is smaller than the second cross-sectional area, in a cross-section perpendicular to the longitudinal axis, a standard vibration anti-node, which is one of vibration anti-nodes (A1, A2, A3, A4), being positioned at the third component by the ultrasonic vibration causing the extending portion to vibrate at a frequency in a predetermined frequency range (Δf), defined as the range between a minimum resonance frequency and a maximum resonance frequency of the vibration transmitting unit, the third component having a region in which the third cross-sectional area is constant in a direction parallel to the longitudinal axis, wherein the extending portion includes a cross-sectional reduction portion which is provided on the proximal side with respect to the first component, and which reduces a cross-sectional area perpendicular to the longitudinal axis towards the distal side to the first cross-sectional area of the first component, and wherein, in a state where the extending portion vibrates at a frequency in the predetermined frequency range (Δf), all of the vibration anti-nodes (A1, A2, A3, A4) are positioned away from the cross-sectional reduction portion in the direction parallel to the longitudinal axis, characterized in that a standard fluctuation width (ΔY), which is a fluctuation width of the standard vibration anti-node in the direction parallel to the longitudinal axis when a resonance frequency is changed in the predetermined frequency range (Δf), is equal to or less than an extending dimension of the third component in the direction parallel to the longitudinal axis.