Abstract: An automatic input threshold selector includes a maximum value level decision circuit, and an input threshold setting circuit. The maximum value level decision circuit decides, among m+1 level layers defined by m maximum value decision levels, a level layer to which the maximum value of an input signal belongs. The input threshold setting circuit sets an input threshold by selecting one of n input threshold candidates in response to the level layer to which the input signal maximum value belongs. These circuits are implemented as a simple combination of a voltage comparator, logic gates and the like. This makes it possible to solve a problem of a conventional automatic input threshold selector in that its circuit scale and power consumption is rather large because it includes a peak-hold circuit and a bottom-hold circuit.