The nuMSM is an extended standard model only with three right-handed neutrinos. The characteristic feature of the model is the masses of additional right-handed neutrino is constrained up to the electroweak scale. By this restriction, we cannot simply apply the leptogenesis scenario to produce the lepton asymmetry for the baryogenesis though sphaleron effect. However, the enough amount of the lepton asymmetry can be produced via another mechanism triggered by right-handed neutrino flavor oscillation. In this talk, I will explain the detail of the mechanism and dependence on the initial condition.