To provide a power generation control device which achieves both securing of a battery charging capacity and reduction in the output of an engine used to drive a power generator.

In an idling-stop vehicle which performs automatic stop/restart of an engine 1 according to operational conditions; the power generation control device of an internal combustion engine comprises a power generator 2 which supplies power which is generated by the power generator driven by the engine 1 to a battery 3 and an in-vehicle electric equipment; power generation voltage controlling means 4 which controls the power generation voltage of the power generator 2; a voltage detecting means 5 which detects the power generation voltage of the power generator 2; a running conditions detecting means 5 which detects the running conditions of a vehicle; and a power generation voltage reducing means 4 which causes the power generation voltage of the power generator to be lower than under running conditions wherein the frequency of idling-stop operation is high, when it is determined from a value detected by the running conditions detecting means that the vehicle is operated under running conditions wherein the frequency of idling-stop operation is low.