Knocking determination apparatus for internal combustion engine

An electronic control unit (30) for determining knocking in an internal combustion engine (11) having an intake injector (22) for injecting fuel into an air intake port (20) and an in-cylinder injector (17) for directly injecting fuel into a combustion chamber (16). Knocking is determined based on an output signal from a knock sensor (33) during a knock determination period. The electronic control unit alters the knock determination period in accordance with the ratio of the amount of fuel injected by the two injectors.