  It is well known that the block Krylov subspace solvers work efficiently for
some cases of the solution of differential equations with multiple right-hand
sides. In lattice QCD calculation of physical quantities on a given
configuration demands us to solve the Dirac equation with multiple sources. We
show that a new block Krylov subspace algorithm recently proposed by the
authors reduces the computational cost significantly without loosing numerical
accuracy for the solution of the O(a)-improved Wilson-Dirac equation.
