A position-adjustable cervical vertebrae support apparatus capable of being installed in a back of a vehicle seat, the cervical vertebrae support apparatus being constructed in the back of the vehicle seat including a seat base, a back, and a headrest, the cervical vertebrae support apparatus comprising: a cervical vertebrae supporting member which is adapted to be located in an installation space part open in upper and front end portions of the back and which supports cervical vertebrae of a driver; a front-back distance adjusting unit in which a mounting plate is brought into close contact with and fastened to a back of the cervical vertebrae supporting member, a left-handed screw rod and a right-handed screw rod are located at a distance from a back of the mounting plate, movable nuts (63 and 64) are disposed around the left-handed screw rod and the right-handed screw rod, respectively, distance adjustment rods are coupled to the movable nuts (63 and 64), also coupled to both sides hinges provided on the back of the mounting plate in a crossed manner and rotatable around a central pin, and the left-handed screw rod and the right-handed screw rod are rotated by a motor, so that, as the distance adjustment rods are rotated in a crossed state by rotation of the left-handed screw rod and the right-handed screw rod by the motor, the cervical vertebrae supporting member is moved forward or backward; and an up-down distance adjusting unit in which a vertical mounting plate is provided to support a side of the motor, a bottom mounting base is provided to support a bottom side of the vertical mounting plate, and a rod coupled to a cylinder is connected to a bottom of the bottom mounting base in order to lift or lower the bottom mounting base, so that the cervical vertebrae supporting member is vertically moved by operation of the cylinder; wherein a plate-shaped front vertical cover portion is formed on a front of a lower end of the cervical vertebrae supporting member a distance of which is adjusted on the back by the front-back distance adjusting unit, a plate-shaped back vertical cover portion is formed at a distance from a back of the front vertical cover portion, and a front support plate portion adapted to extend vertically from a top of a front of the back is inserted between the front vertical cover portion and the back vertical cover portion, so that the front support plate portion is brought into close contact with inner surfaces of the front vertical cover portion and the back vertical cover portion by forward and backward movement of the front vertical cover portion and the back vertical cover portion, and thus forward and backward movement of the cervical vertebrae supporting member is limited. a cervical vertebrae supporting member which is adapted to be located in an installation space part open in upper and front end portions of the back and which supports cervical vertebrae of a driver; a front-back distance adjusting unit in which a mounting plate is brought into close contact with and fastened to a back of the cervical vertebrae supporting member, a left-handed screw rod and a right-handed screw rod are located at a distance from a back of the mounting plate, movable nuts (63 and 64) are disposed around the left-handed screw rod and the right-handed screw rod, respectively, distance adjustment rods are coupled to the movable nuts (63 and 64), also coupled to both sides hinges provided on the back of the mounting plate in a crossed manner and rotatable around a central pin, and the left-handed screw rod and the right-handed screw rod are rotated by a motor, so that, as the distance adjustment rods are rotated in a crossed state by rotation of the left-handed screw rod and the right-handed screw rod by the motor, the cervical vertebrae supporting member is moved forward or backward; and an up-down distance adjusting unit in which a vertical mounting plate is provided to support a side of the motor, a bottom mounting base is provided to support a bottom side of the vertical mounting plate, and a rod coupled to a cylinder is connected to a bottom of the bottom mounting base in order to lift or lower the bottom mounting base, so that the cervical vertebrae supporting member is vertically moved by operation of the cylinder; wherein a plate-shaped front vertical cover portion is formed on a front of a lower end of the cervical vertebrae supporting member a distance of which is adjusted on the back by the front-back distance adjusting unit, a plate-shaped back vertical cover portion is formed at a distance from a back of the front vertical cover portion, and a front support plate portion adapted to extend vertically from a top of a front of the back is inserted between the front vertical cover portion and the back vertical cover portion, so that the front support plate portion is brought into close contact with inner surfaces of the front vertical cover portion and the back vertical cover portion by forward and backward movement of the front vertical cover portion and the back vertical cover portion, and thus forward and backward movement of the cervical vertebrae supporting member is limited.