An engine ECU executes a program including a step(S104) of calculating coefficient of correlation K that is a value related to a deviation between a vibration waveform and a knock waveform model by comparing the engine's vibration waveform with the knock waveform model stored in advance at a plurality of timings, a step(S106) of calculating a knock intensity N as based on a largest coefficient ofcorrelation K among the calculated coefficient of correlation Ks, a step(S110) of determining that the engine knocks if knock intensity N is larger than a predetermined reference value (YES at S 108 ), and a step of determining that the engine does not knock if knock intensity N is not larger than a predetermined reference value (NO at S 108 ).