An engine ECU executes a program including the steps of: calculating a magnitude value LOG(V) by logarithmically converting a magnitude V of vibration occurring in an engine, calculating a median V(50) and a standard deviation σ of magnitude values LOG(V); and setting, to the product of the standard deviation σ and a factor A, a first upper limit of a determination value V(KX) that is to be compared with a knock magnitude N for determining whether or not knocking has occurred, and setting a first lower limit of the determination value V(KX) to the product of the standard deviation σ and a factor B.