A method for configuring a master/slave board during initial booting of dual boards, and dual boards thereof are proposed. Each of the dual boards includes: a voltage input part to which an AC voltage is applied by initial booting; a voltage converter for converting the applied AC voltage into a DC voltage; a communication part for transmitting a DC voltage value corresponding to the converted DC voltage to a counterpart board and receiving a DC voltage value of the counterpart board from the counterpart board; and a controller for initializing the voltage converter when an initial boot signal and the AC voltage are applied from outside, converting the DC voltage converted by the voltage converter into the DC voltage value, and comparing the DC voltage values of each board transmitted and received through the communication part, so as to configure each board as a master or slave board.