A first jet tab and a second jet tab are symmetrically arranged with respect to a symmetry plane and have a symmetrical shape with respect to the symmetry plane, and are symmetrically driven with respect to the symmetry plane by a driving section. A distance between a tip of the first jet tab and a first rotation axis is larger than a distance between the first rotation axis and the symmetry plane. A distance between a tip section of the second jet tab and a second rotation axis is larger than a distance between the second rotation axis and the symmetry plane.