a logic circuit for outputting signals corresponding to an input signal depending on a clock signal sent from an external source includes at least one synchronous flip - flop being synchronized with the clock signal , so that the flip - flop latches the input signal , and a unit for controlling an input of the clock signal to the flip - flop based on a difference between logic levels of an output signal of the flip - flop and an input signal newly latched by the flip - flop .