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 exhibi
ts 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.
