An ethanol engine system stabilizes components of reformed gas generated by a reformer and a calorific value of fuel supplied to an engine. The ethanol engine system includes a reservoir tank for an aqueous ethanol solution, a first supply device that supplies the aqueous ethanol solution to the reformer, a separator that cools mixed gas fed from the reformer, including the reformed gas, condenses water vapor included in the mixed gas and separates into gas and liquid, a reformed gas supply device that supplies the reformed gas separated by the separator to the engine, a recovery tank that collects a recovery solution separated by the separator, and a first recovery solution supply device that supplies the recovery solution in the recovery tank to the reformer or a second recovery solution supply device that supplies the recovery solution in the recovery tank to a combustion chamber of the engine.