My main research object is a projective manifold, which is a submanifold of the complex projective space. Especially, I study the structure of projective manifolds whose tangent bundles or cotangent bundles have semipositive curvature by using the techniques of complex geometry, algebraic geometry, several complex variables, and so on. I have researched the structure of projective manifolds whose tangent bundles are semipositive by using the theory of singular Hermitian metrics. Finally, I established the structure theorem of semipositive foliations. Now, I'm studying the structure of projective manifolds whose cotangent bundles are semipositive.