To provide an engine system excellent in system efficiency and increased in the exhaust heat recovery quantity and combustion efficiency of an engine by increasing the reforming efficiency of a reformer in an engine system with the reformer. In the engine system with the reformer provided with the reformer and driving an engine, using after-reformation fuel obtained by reforming before-reformation fuel with the reformer as one of fuel, a before-reformation fuel supply quantity adjusting device adjusting a supply quantity of the before-reformation fuel supplied to the reformer and an after-reformation fuel supply quantity adjusting device adjusting a supply quantity of the after-reformation fuel supplied to the engine are connected to the reformer, and the reformer is installed adjacently to an engine combustion chamber via the after-reformation fuel supply quantity adjusting device.