1. A calculation device for deriving solutions of a system of linear equations, which realizes a solution of the system of linear equations using an iterative method belonging to a Krylov subspace method, the device comprising: a plurality of arithmetic units, wherein a vector sequence x k , where k is a natural number containing 0, approximating to the solution of the system of linear equations comprises a plurality of components in accordance with an order of the vector sequence x k , when the vector sequence x k is divided into a plurality of different regions corresponding to the plurality of components and each of the plurality of arithmetic units are caused to execute arithmetic processings corresponding to the plurality of different regions in parallel in iterative computation of causing the vector sequence x k to approximate to the solutions, a preconditioned matrix that is used in the iterative computation is a diagonal matrix, the plurality of arithmetic units are a combination of a plurality of cores provided in one multicore CPU, a combination of a plurality of cores provided in one GPU, a combination of a plurality of CPUs, a combination of a plurality of GPUs, a combination of a CPU and a GPU, or a combination of a plurality of computers, the iterative method is a preconditioned conjugate gradient method using a diagonal matrix M −1 as the preconditioned matrix, and when a solution vector x of a system of linear equations Ax=b constituted by a known matrix A and a known vector b is derived, the vector sequence x k is caused to approximate to the solution vector x by preparing the vector sequence x k , vector sequences r k and p k , and scalar sequences α k and β k , using recurrence formulae as indicated in expression 1: r 0 = b - Ax 0 p 0 = M - 1 ⁢ r 0 α k = ( r k , M - 1 ⁢ r k ) ⁢ / ⁢ ( p k , Ap k ) x k + 1 = x k + α k ⁢ p k r k + 1 = r k - α k · Ap k β k = ( r k + 1 , M - 1 ⁢ r k + 1 ) ⁢ / ⁢ ( r k , M - 1 ⁢ r k ) p k + 1 = M - 1 ⁢ r k + 1 + β k ⁢ p k }. Expression ⁢ ⁢ 1