An electro-mechanical brake with a differential gear that is attached to one side of a brake disc provided inside vehicle wheels to selectively reduce or stop rotations of the vehicle wheels along with an operation of a brake pedal by a user, the brake comprising: a driving unit that generates a rotational force by a power that is selectively applied along with the operation of the brake pedal by the user; a differential gear unit that is connected to the driving unit through a gear and in which a first shaft and a second shaft that are disposed in a straight line to serve as a rotational shaft are rotated in the same direction by the rotational force provided by the driving unit; an external braking unit that is connected to the first shaft of the differential gear unit through a gear to provide a braking power to an outer surface of the disc along with the rotation of the first shaft of the differential gear unit; and an internal braking unit that is connected to the second shaft of the differential gear unit through a gear to provide a braking power to an inner surface of the disc along with the rotation of the second shaft of the differential gear unit, wherein when the driving unit is driven, the rotational force of the driving unit is transmitted to the differential gear unit, and the external braking unit and the internal braking unit that are connected to the differential gear unit simultaneously provide the braking powers to the disc along with the rotation of the differential gear unit, characterized in that the differential gear unit includes: a ring gear that meshes with a driving gear of the driving unit to be rotated by a rotational force provided by the driving gear; a 'U'-shaped differential gear case that is integrally formed on one surface of the ring gear to be rotated together with the ring gear around a rotational shaft of the ring gear along with the rotation of the ring gear; a pair of differential side gears that is disposed to face each other within the differential gear case to connect one ends of the first shaft and the second shaft that are disposed in a straight line to serve as the rotational shaft of the ring gear; a pair of differential pinion gears that vertically meshes with the pair of differential side gears and is disposed to face each other within the differential gear case; an inner pinion gear that is provided at an outer portion of the first shaft to transmit a rotational force of the first shaft rotated along with the rotation of the ring gear; and an outer pinion gear that is provided at an outer portion of the second shaft to transmit a rotational force of the second shaft rotated along with the rotation of the ring gear. a driving unit that generates a rotational force by a power that is selectively applied along with the operation of the brake pedal by the user; a differential gear unit that is connected to the driving unit through a gear and in which a first shaft and a second shaft that are disposed in a straight line to serve as a rotational shaft are rotated in the same direction by the rotational force provided by the driving unit; an external braking unit that is connected to the first shaft of the differential gear unit through a gear to provide a braking power to an outer surface of the disc along with the rotation of the first shaft of the differential gear unit; and an internal braking unit that is connected to the second shaft of the differential gear unit through a gear to provide a braking power to an inner surface of the disc along with the rotation of the second shaft of the differential gear unit, wherein when the driving unit is driven, the rotational force of the driving unit is transmitted to the differential gear unit, and the external braking unit and the internal braking unit that are connected to the differential gear unit simultaneously provide the braking powers to the disc along with the rotation of the differential gear unit, a ring gear that meshes with a driving gear of the driving unit to be rotated by a rotational force provided by the driving gear; a 'U'-shaped differential gear case that is integrally formed on one surface of the ring gear to be rotated together with the ring gear around a rotational shaft of the ring gear along with the rotation of the ring gear; a pair of differential side gears that is disposed to face each other within the differential gear case to connect one ends of the first shaft and the second shaft that are disposed in a straight line to serve as the rotational shaft of the ring gear; a pair of differential pinion gears that vertically meshes with the pair of differential side gears and is disposed to face each other within the differential gear case; an inner pinion gear that is provided at an outer portion of the first shaft to transmit a rotational force of the first shaft rotated along with the rotation of the ring gear; and an outer pinion gear that is provided at an outer portion of the second shaft to transmit a rotational force of the second shaft rotated along with the rotation of the ring gear.