  In the paper the Schr\"odinger equation for quasibound resonance state with
complex energy is considered. The system of inhomogeneous differential
equations is obtained for the real and imaginary parts of wave function. On the
base of known solution of corresponding homogeneous equation, the inhomogeneus
system is solved with help of iteration procedure. The single-particle neutron
$2p$-state in the Woods - Saxon potential is analyzed for $^{13}C$ nucleus.
