A power supply control apparatus is provided with: a first calculating device configured to calculate a vehicle stop time rate on the basis of a travel history of the vehicle; a second calculating device configured to calculate a stoppable time rate on the basis of the travel history, and an estimating device configured to estimate an electric power amount associated with the idling stop control, on the basis of the calculated stoppable time rate if the idling stop control is allowed when the vehicle decelerates, and to estimate the electric power amount, on the basis of the calculated vehicle stop time rate if the idling stop control is not allowed when the vehicle decelerates.