  We theoretically propose a principle for precise measurement of oscillatory
domain wall (DW) by a ferromagnetic Josephson junction, which is composed of a
ferromagnetic wire with DW and two superconducting electrodes. The
current-voltage curve exhibits stepwise structures, only when DW oscillates in
the ferromagnetic wire. The voltage step appears at V = n(\hbar/2e)\omega_DW
with the fundamental constant \hbar/e, integer number n, and the DW frequency
\omega_DW. Since V can be determined in the order of 10^9 accuracy, the
oscillatory DW will be measured more precisely than present status by
conventional method.
