An internal combustion engine to which the apparatus is applied is a multi-cylinder internal combustion engine that includes a passage injection valve and a cylinder injection valve and that can use gasoline and alcohol as fuel. The apparatus performs abnormality determination for a determination object device, based on a detection signal of an oxygen sensor provided in an exhaust passage of the internal combustion engine. The concentration sensor detects alcohol concentration ALp of the fuel in a first fuel passage through which the fuel is fed to the passage injection valve, and alcohol concentration ALd of the fuel in a second fuel passage through which the fuel is fed to the cylinder injection valve. When a difference ΔAL between the alcohol concentrations ALp, ALd is a determination value or greater (S13: YES), the execution of the abnormality determination is prohibited (S12).