A machine tool electrical driving system comprising: a housing; a hollow tubular spindle extending in a front-rear direction in the housing and rotatably installed with respect to the housing; a drive pulley fixedly installed to the spindle outside a rear portion of the spindle; a spindle motor configured to rotate the drive pulley; a chuck installed in a front end portion of the spindle and having a jaw clamping a workpiece; a drawbar installed to be linearly movable inside the spindle in a front-rear direction so that a front end portion is connected to the chuck to be linearly movable with respect to the chuck but non-rotatable relative to the chuck in the front-rear direction; a motion conversion unit configured to receive a rotational force of the drive pulley and convert the rotation force into a forward-rearward motion of the drawbar; a chuck locking unit configured to restrain or release a rotary motion of the chuck with respect to the housing; a clutch unit installed to be movable forward or rearward between a front portion of the spindle and a rear portion of the chuck and connecting the spindle to the chuck or separating the spindle from the chuck so that the spindle is rotatable relative to the chuck; and an encoder unit configured to detect a rotation position of the drive pulley characterized in that the motion conversion unit includes: a lead screw having an outer surface on which a screw thread is spirally formed and formed to be fixed to the drawbar, a carrier member having an inner peripheral surface on which a screw thread spirally coupled to the screw thread of the lead screw is formed and coupled to an outside of the lead screw, and a rotational force transmission unit configured to transmit a rotational force of the drive pulley to the carrier member, wherein the rotational force transmission unit includes a ring-shaped drive member fixedly connected to the drive pulley and a plurality of drive pins installed in the drive member to protrude radially inward to transmit a rotational force to the carrier member, and a long hole-shaped backlash groove into which a distal end of the drive pin is inserted to move by a certain amount in a circumferential direction is formed on an outer surface of the carrier member. a housing; a hollow tubular spindle extending in a front-rear direction in the housing and rotatably installed with respect to the housing; a drive pulley fixedly installed to the spindle outside a rear portion of the spindle; a spindle motor configured to rotate the drive pulley; a chuck installed in a front end portion of the spindle and having a jaw clamping a workpiece; a drawbar installed to be linearly movable inside the spindle in a front-rear direction so that a front end portion is connected to the chuck to be linearly movable with respect to the chuck but non-rotatable relative to the chuck in the front-rear direction; a motion conversion unit configured to receive a rotational force of the drive pulley and convert the rotation force into a forward-rearward motion of the drawbar; a chuck locking unit configured to restrain or release a rotary motion of the chuck with respect to the housing; a clutch unit installed to be movable forward or rearward between a front portion of the spindle and a rear portion of the chuck and connecting the spindle to the chuck or separating the spindle from the chuck so that the spindle is rotatable relative to the chuck; and an encoder unit configured to detect a rotation position of the drive pulley characterized in that the motion conversion unit includes: a lead screw having an outer surface on which a screw thread is spirally formed and formed to be fixed to the drawbar, a carrier member having an inner peripheral surface on which a screw thread spirally coupled to the screw thread of the lead screw is formed and coupled to an outside of the lead screw, and a rotational force transmission unit configured to transmit a rotational force of the drive pulley to the carrier member, wherein the rotational force transmission unit includes a ring-shaped drive member fixedly connected to the drive pulley and a plurality of drive pins installed in the drive member to protrude radially inward to transmit a rotational force to the carrier member, and a long hole-shaped backlash groove into which a distal end of the drive pin is inserted to move by a certain amount in a circumferential direction is formed on an outer surface of the carrier member. a lead screw having an outer surface on which a screw thread is spirally formed and formed to be fixed to the drawbar, a carrier member having an inner peripheral surface on which a screw thread spirally coupled to the screw thread of the lead screw is formed and coupled to an outside of the lead screw, and a rotational force transmission unit configured to transmit a rotational force of the drive pulley to the carrier member, wherein the rotational force transmission unit includes a ring-shaped drive member fixedly connected to the drive pulley and a plurality of drive pins installed in the drive member to protrude radially inward to transmit a rotational force to the carrier member, and a long hole-shaped backlash groove into which a distal end of the drive pin is inserted to move by a certain amount in a circumferential direction is formed on an outer surface of the carrier member.