A lateral sealing device for a packaging machine for sandwiching and laterally sealing a packaging material along a sealing direction intersecting a conveying direction of the packaging material, the lateral sealing device of a packaging machine comprising: a pair of rotating bodies (50a, 50b), each of the rotating bodies including a horn assembly and an anvil (51b, 52a), the horn assembly including a horn (51a, 52b), a plurality of vibrating elements (511, 521) and a plurality of resonators, each of the rotating bodies being rotatable about a rotation axis (C1, C2), each rotating body having a forward side and a reverse side relative to a direction of rotation about the rotation axis; and a securing member adapted to grip the horn assembly at the forward side and the reverse side thereof, and to secure the horn assembly to the rotating bodies (50a, 50b); wherein the horn (51a, 52b) is mounted on the rotating body and the peripheral members thereof; and a plurality of vibration elements (511, 521) are coupled so as to line up at equidistant intervals along the sealing direction behind the horn; characterized in that the securing member is provided with a plurality of resonators, a holding part, and a securing part, the plurality of resonators being coupled to the horn (51a, 52b) in adjacent positions so as to sandwich the vibrating elements (511, 521) from two sides, the holding part holding the plurality of resonators, and the securing part securing the holding part; and the lateral sealing device is configured such that a node of ultrasonic vibrations is centrally positioned in the major axis direction of each resonator, and the vicinity of the node is held in place to secure the corresponding rotating body (50a, 50b). a pair of rotating bodies (50a, 50b), each of the rotating bodies including a horn assembly and an anvil (51b, 52a), the horn assembly including a horn (51a, 52b), a plurality of vibrating elements (511, 521) and a plurality of resonators, each of the rotating bodies being rotatable about a rotation axis (C1, C2), each rotating body having a forward side and a reverse side relative to a direction of rotation about the rotation axis; and a securing member adapted to grip the horn assembly at the forward side and the reverse side thereof, and to secure the horn assembly to the rotating bodies (50a, 50b); wherein the horn (51a, 52b) is mounted on the rotating body and the peripheral members thereof; and a plurality of vibration elements (511, 521) are coupled so as to line up at equidistant intervals along the sealing direction behind the horn; characterized in that the securing member is provided with a plurality of resonators, a holding part, and a securing part, the plurality of resonators being coupled to the horn (51a, 52b) in adjacent positions so as to sandwich the vibrating elements (511, 521) from two sides, the holding part holding the plurality of resonators, and the securing part securing the holding part; and the lateral sealing device is configured such that a node of ultrasonic vibrations is centrally positioned in the major axis direction of each resonator, and the vicinity of the node is held in place to secure the corresponding rotating body (50a, 50b).