A built-in type electric driving system of a machine tool, comprising: a housing; a hollow tube-shaped spindle extending from the housing in forward and backward directions and rotatably installed on the basis of the housing; a built-in motor consisting of a stator fixed to the inside of the housing and a rotor fixed to an outer surface of the spindle, and configured to generate torque between the stator and the rotor by power applied from the outside to cause rotation of the rotor; a chuck installed at a front end of the spindle and including a jaw configured to grip a workpiece; a drawbar installed at an inner side of the spindle to be linearly movable in the forward and backward directions, and having a front end connected to the jaw; a drawbar key and a drawbar key groove configured to connect the drawbar to the chuck so that the drawbar is linearly movable, but not rotatable; a lead screw formed with a thread in a spiral shape on an outer surface thereof, and formed to be fixed to the drawbar; a driving unit fixed to the outer surface of the spindle to rotate together with the spindle; a female screw cover coupled to the driving unit to rotate together with the driving unit, and having a thread formed on an inner circumferential surface thereof to be screw-coupled to the thread of the lead screw (4:); and characterised by a chuck locking unit configured to restrict or release the rotational movement of the chuck on the basis of the housing; and a clutch unit installed to be movable in the forward and backward directions between a front portion of the spindle and a rear portion of the chuck to restrict the spindle relative to the chuck or separate the spindle so that the spindle is rotatable relative to the chuck. a housing; a hollow tube-shaped spindle extending from the housing in forward and backward directions and rotatably installed on the basis of the housing; a built-in motor consisting of a stator fixed to the inside of the housing and a rotor fixed to an outer surface of the spindle, and configured to generate torque between the stator and the rotor by power applied from the outside to cause rotation of the rotor; a chuck installed at a front end of the spindle and including a jaw configured to grip a workpiece; a drawbar installed at an inner side of the spindle to be linearly movable in the forward and backward directions, and having a front end connected to the jaw; a drawbar key and a drawbar key groove configured to connect the drawbar to the chuck so that the drawbar is linearly movable, but not rotatable; a lead screw formed with a thread in a spiral shape on an outer surface thereof, and formed to be fixed to the drawbar; a driving unit fixed to the outer surface of the spindle to rotate together with the spindle; a female screw cover coupled to the driving unit to rotate together with the driving unit, and having a thread formed on an inner circumferential surface thereof to be screw-coupled to the thread of the lead screw (4:); and characterised by a chuck locking unit configured to restrict or release the rotational movement of the chuck on the basis of the housing; and a clutch unit installed to be movable in the forward and backward directions between a front portion of the spindle and a rear portion of the chuck to restrict the spindle relative to the chuck or separate the spindle so that the spindle is rotatable relative to the chuck. a chuck locking unit configured to restrict or release the rotational movement of the chuck on the basis of the housing; and a clutch unit installed to be movable in the forward and backward directions between a front portion of the spindle and a rear portion of the chuck to restrict the spindle relative to the chuck or separate the spindle so that the spindle is rotatable relative to the chuck.