When an engine restart request is given in an engine stopping period which begins at a point of fuel supply interruption and ends at a point of complete engine stop, an engine starting system judges whether TDC engine speed detected immediately before is equal to or lower than a specific value “A”, the counted number of reverse running motions of the engine is 0, and a piston in an expansion stroke cylinder is relatively close to TDC. If the judgment result is in the affirmative with all these conditions satisfied, the engine starting system injects fuel into the expansion stroke cylinder and then ignites and combusts a mixture produced therein. The engine starting system also injects the fuel into a compression stroke cylinder and then ignites and combusts a mixture produced therein when a piston in the compression stroke cylinder has gone beyond TDC.