  We propose a practical method to solve the random-phase approximation (RPA)
in the self-consistent Hartree-Fock (HF) and density-functional theory. The
method is based on numerical evaluation of the residual interactions utilizing
finite amplitude of single-particle wave functions. The method only requires
calculations of the single-particle Hamiltonian constructed with independent
bra and ket states. Using the present method, the RPA calculation becomes
possible with a little extension of a numerical code of the static HF
calculation. We demonstrate usefulness and accuracy of the present method
performing test calculations for isoscalar responses in deformed 20Ne.
