Provided is an
adder in which all of circuits can be constituted by
CMOS transistors, a process is simplified, and a
chip size can be reduced as compared with a conventional art. The
adder according to the present invention includes: a first VI converter and a second VI converter that allow a current corresponding to an input
voltage to flow therein; and a current addition
resistor having one end commonly connected to output terminals of the first VI converter and the second VI converter and another end grounded, which is adjustable in a resistance value. Each of the first VI converter and the second VI converter includes: a prestage VI converter that generates a
reference current; a poststage VI converter that generates a current corresponding to the input
voltage; a first
current mirror circuit whose first terminal on a reference side is connected with the prestage VI converter and whose first output terminal in which a current corresponding to the first terminal flows is connected with the poststage VI converter; and a second
current mirror circuit whose second terminal on the reference side is connected to the first output terminal, and which can adjust a current ratio from a second output terminal in correspondence with the current that flows in the second terminal. A
voltage at the one end of the current addition
resistor is output as an addition voltage.