An engine ECU executes a program including the steps of: calculating a coefficient of correlation K in accordance with a result of comparing a waveform of a vibration of a frequency band including a resonance frequency of an engine with a knock waveform model previously created as a waveform of a vibration caused when the engine knocks (S112); calculating a knock intensity N from an intensity of a vibration of a frequency band excluding the resonance frequency of the engine (S114); if knock intensity N is larger than a reference value and coefficient of correlation K is larger than a threshold value (YES at S116), determining that the engine knocks (S118); and if knock intensity N is smaller than the reference value and/or coefficient of correlation K is smaller than the threshold value, determining that the engine does not knock (S122).