An electric power generation control system has an electric power generation amount determining section for determining an electric power generation request amount of a vehicle alternator by monitoring vehicle conditions, an electric power generation amount increase judgment section for judging presence/absence of an electric power generation amount increase request to the vehicle alternator based on change of the electric power generation request amount in passage of time, an idle state judgment section for judging whether or not a vehicle engine falls in idle operation state, and an electric power generation amount suppressing control section for suppressing an electric power generation amount of the vehicle alternator. In the idle operation state of the vehicle engine and the presence of the electric power generation amount increase request, the electric power generation amount suppressing control section halts the control of suppressing the electric power generation of the vehicle alternator.