An inspection apparatus for inspecting a phase modulated wobble track of an optical disk is provided. A radial push-pull signal (a wobble signal) of an optical disk is supplied to a low pass filter where a phase boundary portion of the wobble signal is smoothed, and then binarized by a binarizer and supplied to a time interval analyzer. The time interval analyzer analyzes a period of the binary wobble signal to extract two peak values T1 and T2 thereof. An operation device computes a difference value of the two periods T1 and T2 and a standard deviation of each peak, and compares each computed value to a threshold value for simultaneously evaluating CNR and a phase shift. The low pass filter and the binarizer may be incorporated into an optical disk apparatus for smoothing the phase boundary portion of the reproduced wobble signal.