An internal combustion engine in which an output from a fuel reformation cylinder is obtained based on a cylinder internal pressure and a rotational speed of the fuel reformation cylinder, and an output adjusting operation for adjusting an output from an output cylinder is executed so that a sum of the output from the fuel reformation cylinder and the output from the output cylinder matches with a required engine power. In this output adjusting operation, during a transient operation in which the required engine power is increased, the output from the output cylinder is increased by increasing the fuel supply amount to a combustion chamber. Then, the fuel supply amount to a fuel reformation chamber is gradually increased while the fuel supply amount to the combustion chamber is gradually reduced, so that a heat source is shifted from the fuel to the reformed fuel.