A device for controlling ISG logic is mounted in a vehicle equipped with an ISG system. The device includes a brake pedal switch, a shift lever switch that shows the current state of a gear of the vehicle, an inclination sensor that is mounted in the vehicle and measures the inclination of a road where the vehicle is positioned, a controller that internally controls the vehicle to an N (Neutral) state, regardless of the gear range shown by the shift lever switch, for the vehicle on a downhill, in accordance with the measured inclination, and an engine unit that performed idle stop when the brake pedal becomes ON, with the gear of the vehicle at a D (Drive) sate, and restarts the stopped engine when the brake pedal becomes OFF, with the gear of the vehicle at the D state.