The Time Dependent Resonating Hartree--Fock (TD Res HF) theory is expected to work better than the usual TDHF one if we describe large-amplitude collective motions in soft nuclei with large quantum fluctuations. To make an essential feature of the TD Res HF theory clear, we apply it to the exactly solvable Lipkin model. We adopt an adiabatic perturbative approach to a solution of the TD Res HF equation and derive inertia parameter of kinetic energy and potential energy of the collective motion.

PACS numbers: 11.30.Rd, 12.39.Ki, 14.40.Aq