PURPOSE: To prevent malfunction in the case of selecting a data signal by using two signal switching control signals.

CONSTITUTION: Data signals D1, D2 are inverted by inverters 1, 2 and inputted to relevant transfer gates 3, 4. On the other hand, signal switching control signals S1, S2 are both inputted to a NOR circuit 5 and its output signal (a) is inputted to an EXNOR circuit 7 and an EXOR circuit 8. Moreover, the signal switching control signal S2 is inverted by an inverter 6 and its output signal (b) is similarly inputted to the EXNOR circuit 7 and an EXOR circuit 8. Output signals A, B of the EXNOR circuit 7 and the EXOR circuit 8 are inputted to the transfer gates 3, 4 and the selection changeover is implemented to the input data signals D1, D2.