To generate flexural oscillation large in amplitude even to large pressure force so as to get large driving force by providing a low rigidity part to lower the rigidity of an elastic body, in the position of the side of the flexural oscillation of the elastic body.

An oscillatory actuator is composed of an elastic body 11 and four piezoelectric substances 12a, 12b, 12p, and 12p' joined with the elastic body 11. Then, primary vertical oscillation and quartic flexural oscillation are generated harmonically in the elastic body 11, and by its degeneracy, the driving force is taken out from the specified position of the elastic body 11. For the elastic body 11, the thickness of the elastic body 11 is thinned at roughly vertically to it longitudinal direction, thus four pieces of grooves 13a-13d to serve as low rigidity parts where the rigidity is lowered are made. These grooves 13a and 13d are made in the positions of the sections A2, A3, A4, and A5 corresponding to the sides of the flexural oscillation, and they have the effect of enlarging the amplitude of the flexural oscillation.