Abstract: In a serial-type A/D converter utilizing folding circuit cells connected in cascade, the cell has a differential type input and a differential type output, and a comparator included in the cell switches over current paths in the cell to establish a folding characteristic. An input potential difference is converted into a current difference by a pair of transistors having the emitters interconnected through a resistor, and the current difference is further converted into a pair of differential output voltages by a load circuit having a pair of series connections each including a resistor, a diode and a transistor having its base connected with another resistor, so that the non-linear characteristic and gain can be corrected.