An apparatus and method for detecting vertical blanking intervals (VBI) is disclosed. The apparatus can identify and filter non-VBI signals, and calculate a level value for digitization corresponding to the type of television signals. The apparatus includes a detecting unit and a coupled computing unit. The detecting unit is for generating a detecting signal according to a television signal. The computing unit is for calculating a slope of the detecting signal, and for determining whether the television signal contains a clock run-in signal according to the slope.