An anvil is provided in an ultrasonic sealing machine, in which vibration applying surfaces of a pair of horns and an abutment surface on an end face of the anvil cooperate with each other to bond a laminate. The abutment surface includes left and right welding surfaces which are disposed in the extending direction of the vibration applying surface and protrude toward the horns to face two vibration applying surfaces. The left and right welding surfaces each have an area per unit length in the extending direction, which continuously or step-wisely increases with an increase in distance from a center of the seal area, which is a region where the two vibration applying surfaces are adjacent to each other.