PURPOSE: To provide a magnitude comparator which has redundancy and in addition, is of the circuit configuration of a small number of elements.

CONSTITUTION: In the magnitude comparator to compare the sizes of two binary numbers A, B of n-bits represented by A=Σ2i-1ai and B=Σ2i-1bi (where Σmeans i=1 to (n) and ai=0, 1, bi=0, 1) this comparator is characterized by being constituted so that it consists of plural pieces of unit circuits to switch two states of a serial state in which an input terminal I and an output terminal O are connected by a transistor Q10 to input the i-th bit ai of A and a parallel state in which the input terminal I and the output terminal O are short-circuited, and this short-circuit point and power supply are connected by the transistor Q10 by using switches (Q11 to 13 and inverter 14) controlled by the value of the i-th bit bi of B, and the unit circuits are connected to a five-stage cascade.