Provided is a replica bias circuit which is suitable for multi-layer stacked CMOS current mode logic (CML) and is stably used in application fields using a low power supply voltage. The replica bias circuit applies a reference voltage to gates of target transistors constituting an electronic circuit. The replica bias circuit includes a sub threshold voltage generator for maintaining a voltage difference lower than a threshold voltage of the transistor; and a replica path including devices designed by referring to dimensions of constituent devices forming a current flow path, the current flow path including the target transistors in the electronic circuit. With the replica bias circuit, multi-layer stacked CMOS current mode logic (CML) circuits can stably operate even at a low power supply voltage.