A steering assist device, comprising: an electric motor that applies a steering driving force to a steering operation mechanism of a vehicle; characterized in that an information obtaining unit that obtains a lateral deviation (y) of the vehicle from a target travel line (Ls), a lateral deviation change rate (dy/dt), or a rate of change in the lateral deviation per unit time, and curvature (ct) of the target travel line (Ls); a steering assist current value setting unit that sets a steering assist current value (Is*) corresponding to a target value of steering assist torque; a main lane keep assist current value setting unit that sets a main lane keep assist current value (Imr*) that generates main lane keep assist torque according to the lateral deviation (y) and the lateral deviation change rate (dy/dt), based on the lateral deviation (y) and the lateral deviation change rate (dy/dt) obtained by the information obtaining unit; a sub lane keep assist current value setting unit that sets a sub lane keep assist current value (Isr*) that generates sub lane keep assist torque according to the curvature (ct), based on the curvature (ct) obtained by the information obtaining unit; a target current value calculation unit that calculates a target current value (I*) by using the steering assist current value (Is*) set by the steering assist current value setting unit, the main lane keep assist current value (Imr*) set by the main lane keep assist current value setting unit, and the sub lane keep assist current value (Isr*) set by the sub lane keep assist current value setting unit; and a control unit that drivingly controls the electric motor based on the target current value (I*) calculated by the target current value calculation unit. an electric motor that applies a steering driving force to a steering operation mechanism of a vehicle; characterized in that an information obtaining unit that obtains a lateral deviation (y) of the vehicle from a target travel line (Ls), a lateral deviation change rate (dy/dt), or a rate of change in the lateral deviation per unit time, and curvature (ct) of the target travel line (Ls); a steering assist current value setting unit that sets a steering assist current value (Is*) corresponding to a target value of steering assist torque; a main lane keep assist current value setting unit that sets a main lane keep assist current value (Imr*) that generates main lane keep assist torque according to the lateral deviation (y) and the lateral deviation change rate (dy/dt), based on the lateral deviation (y) and the lateral deviation change rate (dy/dt) obtained by the information obtaining unit; a sub lane keep assist current value setting unit that sets a sub lane keep assist current value (Isr*) that generates sub lane keep assist torque according to the curvature (ct), based on the curvature (ct) obtained by the information obtaining unit; a target current value calculation unit that calculates a target current value (I*) by using the steering assist current value (Is*) set by the steering assist current value setting unit, the main lane keep assist current value (Imr*) set by the main lane keep assist current value setting unit, and the sub lane keep assist current value (Isr*) set by the sub lane keep assist current value setting unit; and a control unit that drivingly controls the electric motor based on the target current value (I*) calculated by the target current value calculation unit.