In a starting system of an internal combustion engine, an injector for injecting fuel directly into a combustion chamber and an ignition plug for igniting an air/fuel mixture in the combustion chamber are provided, and a throttle device is provided in an intake pipe. During stopping of the engine, the starting system operates the throttle device to open a throttle valve to a predetermined throttle opening at a throttle opening speed that is set based on the intake pressure. Upon a start of the engine, the starting system actuates the injector to inject the fuel into a cylinder that is in the expansion stroke, and actuates the ignition plug to ignite the mixture in the combustion chamber.