A combustion system includes a reformer reforming a fuel on a catalyst to increase a combustion energy generated by the fuel per unit quantity of the fuel. The system includes an injection unit injecting a reformed fuel and a non-reformed fuel in such a manner that the reformed fuel is annularly distributed along an inner circumferential wall of a cylinder and the non-reformed fuel is distributed inside of the annularly distributed reformed fuel. The reformed fuel and the non-reformed fuel are combusted in a combustion chamber of the internal combustion engine at a substantially same time. The reformed fuel is annularly distributed along an inner circumferential wall of an internal combustion engine. The non-reformed fuel is distributed in a center portion of the annularly distributed reformed fuel. The non-reformed fuel is compressed self-ignited to be combusted and the reformed fuel is ignited by a combustion of the non-reformed fuel.