To obtain stable oscillation detection values regardless of disturbances and to quantitatively determine whether a knocking detector is normal or not.

At inspection on the knocking detector 52 installed in a cylinder block of an engine, the cylinder block is shaken by a shaking unit 51 via a housing connected to the cylinder block. The performance of the knocking detector 52 is judged on the basis of whether a peak value of voltage variation values, detection values of the knocking detector 52, is greater than a threshold value set on the basis of a reference peak value of test voltage variation values or not.