By making a folded waveform of a folding circuit sharp, the number of elements used in an ADC is reduced and less power consumption is achieved. A folding circuit is composed of a plurality of master-comparator latches, a pair of wiring means for master-to-slave connection, and a slave latch. By means of the wiring means, the non-inverted outputs and the inverted outputs of the master-comparators latches are alternately drawn in the order of magnitude of reference voltages, superimposed, and fed into a pair of inputs of the slave latch. A Gray code signal is directly encoded by an encoder according to the output of the slave latch. A folded signal, which is the output of the folding circuit, takes a sharp waveform. The number of slave latches can be reduced. No XOR gates are required.