Simons [20] proved that there is no closed stable minimal submanifold in the unit sphere, and that there is no closed stable minimal hypersurface in any Riemannian manifold with positive Ricci curvature. Complete stable minimal surfaces in 3-dimensional Riemannian manifolds with nonnegative scalar curvature were discussed by Fischer-Colbrie and Schoen [5], and complete stable minimal hypersurfaces in the Euclidean space were discussed by do Carmo and Peng [3]. In Section 2 of this paper we deal with the nonexistence problem for some complete stable minimal submanifolds in the unit sphere and some complete stable minimal hypersurfaces in a Riemannian manifold with nonnegative Ricci curvature. In Section 3 we consider an application of the nonexistence argument to the free boundary problem of minimal surfaces.The examples of complete non-compact minimal surfaces in the 3 and 5-dimensional unit sphere are obtained by use of the method in [9]. In [6] and [14] uncountably many examples of complete non-compact minimal hypersurfaces in the unit sphere are constructed.In this paper all manifolds are smooth, connected, and have dimensions not less than 2. We shall use the same < , > to denote the inner products on fibers of vector bundles of Riemannian manifolds. We denote by λ λ (M) the greatest lower bound of the spectrum of the Laplacian of a Riemannian manifold M.The author would like to express his hearty thanks to Prof. S. Tanno for his constant encouragement and advice, and to the referee for his useful comments.