Abstract: An apparatus detects the number of tracks traversed on an optical disk. The apparatus includes a differentiation part for differentiating an output signal of a bandpass filter provided on an adjacent stage which eliminates a low DC component, a high frequency component and noise of an inputted modulation signal. A sample trigger generating circuit generates top and bottom signals in response to a data signal outputted through the differentiation part and a signal outputted through a comparator. A top hold part and a bottom hold part holds the data signal at top and bottom. A subtraction part performs a subtraction to obtain a difference between the top and bottom signals outputted from the top and bottom hold parts, thereby resulting in counting the number of the tracks traversed, while increasing a jumping speed required for a detection of the number of the tracks traversed.