An engine ECU executes a program including a step of, when it has temporarily been determined that knocking had occurred because of the presence of an integrated value greater than a product of the reference magnitude and coefficient Y among the integrated values of vibration in fourth frequency band D that includes first to third frequency bands A to C, calculating knock magnitude N using the integrated values in the synthesized waveform of first to third frequency bands A to C and correlation coefficient K calculated from a vibration waveform of fourth frequency band D. Based on a comparison between knock magnitude N and determination value V(KX), whether or not knocking has occurred is determined. If there is no integrated value greater than a product of the reference magnitude and coefficient Y, it is determined that knocking has not occurred.