We discuss ultralight ALP dark matter and its possible connection to primordial magnetic field. When ALP dark matter couples to photon, its oscillation could produce magnetic field via parametric resonance. Unfortunately, this is insufficient to explain the observed magnetic field in large scale structures of our universe. A primary obstacle is placed by the conductivity of the plasma in early universe. By introducing dark photon, we show that the primordial magnetic field of 10^{-24} G with a coherent length ~kpc can be produced from the oscillation of ALP dark matter. This could provide a seed for galactic magnetic field at present universe. This mechanism works for ALP mass smaller than 10^{-17} eV, which indicates that the mechanism takes place after the electron-positron annihilation in the early universe.