A failsafe steering device for a steer-by-wire system includes a main Electronic Control Unit (ECU) that detects manipulating states of a main steering wheel and a rack mechanism via a plurality of sensors, actuates a reaction motor that provides the reaction force to the main steering wheel in relation to a driver's steering force, and controls a steering motor that executes the steering by actuating the rack mechanism. The failsafe steering device further includes a battery providing power to the steering motor, a relay restraining the power supply between the battery and the steering motor, a failsafe ECU that determines the malfunction state of the main ECU and controls the relay accordingly, and a steering shaft that transmits the rotational force of a supplement steering wheel to the rack mechanism.