Provided is an ultrasonic welding device that allows simplifying the configuration and control for causing an ultrasonic horn and an anvil approach each other and move away from each other. The displacement mechanism includes: an urging mechanism that urges an anvil roller (10) toward an ultrasonic horn (6) in such a manner that output surfaces (6e) and a welding surface (10d) move closer in the normal direction thereof； and a pressed member (18) that has guide surfaces (21a, 23a) against which the outer surface of the anvil roller (10), positioned within non-welding areas (E2, E4), are pressed by an urging force of the urging mechanism, the pressed member (18) being fixed to a sheet holding roller (5) in a state where a pressed surface (21a) is disposed within the width-direction range of a slit (6d). In response to the movement of the anvil roller (10) from a welding area (E3) to the non-welding areas (E2, E4), the guide surfaces (21a, 23a) of the pressed member (18) guide the anvil roller (10) in a direction in which the output surfaces (6e) and the welding surface (10d) move away from each other.
