An electric power generation control apparatus has a bridge circuit, a voltage detection circuit, an electric generation control circuit, and an operation mode setting circuit. The bridge circuit has power transistors and diodes through which a field current is supplied to a vehicle alternator driven by a vehicle engine. The voltage detection circuit outputs an instruction signal regarding ON and OFF of supply of the field current so that the output voltage of the vehicle alternator becomes an adjusting voltage. The electric generation control circuit controls the ON and OFF of the power transistors according to the instruction signal from the voltage detection circuit. The operation mode setting circuit selects one of a field wheeling mode and a regenerative mode based on the OFF state of one power transistor, and also selects the regenerative mode when receiving a generation halt instruction form an ECU in the vehicle.