To provide an ultrasonic welding device capable of reducing vibration and noise caused by movement of an anvil. The ultrasonic welding device (1) includes a rotary support mechanical assembly rotatable about a rotation axis (L1) and operable to support a sheet (W) over a circumference centered on the rotation axis (L1), the sheet (W) being continuously supplied; a horn (14) and an anvil (15) attached to the rotary support mechanical assembly to thereby revolve about the rotation axis (L1) and sandwich the sheet (W) supported over the rotary support mechanical assembly to weld the sheet (W); a cam drum (3) and a cam follower (23) for driving the anvil (15) in such a manner that the anvil (15) moves relative to the horn (14); a holding member body (24a); and a power transmission mechanism (7) for distributing a power generated by the cam (3) and the cam follower (23) in such a manner the power is transmitted the anvil (15) and holding member body (24a) in opposite directions.