An electrically driven chucking system comprising an automatic clutch system, comprising: a housing fixedly installed on a main body of a machine tool; a spindle having a hollow tube shape and provided inside the housing to be rotatable with respect to the housing; a driving member disposed outside a rear portion of the spindle to be rotatable relative to the spindle; a spindle motor configured to rotate the driving member; a clutch member which is installed on an outer surface of the spindle to be linearly movable in an axial direction with respect to the spindle 20 between the driving member and one end portion of the housing and which is coupled to the driving member or the housing depending on a direction of movement thereof to selectively connect the spindle to one among the driving member and the housing; a clutch drive unit configured to actuate the clutch member; a drawbar which is formed inside the spindle to permit linear movement thereof in an axial direction with respect to the spindle but preclude rotational movement thereof relative to the spindle, such that the drawbar linearly moves in the axial direction with respect to the spindle or moves together with the spindle depending on the spindle restriction conditions set by the clutch member; an encoder configured to measure an amount of rotation of the spindle; and an encoder rotation device connected to the clutch member and the encoder to transmit a rotational force of the clutch member to the encoder when the clutch member rotates together with the spindle, characterized in that the encoder rotation device comprises a spindle encoder pulley coupled to the clutch member and rotating together with the clutch member, an encoder pulley connected to a shaft of the encoder, and a belt wound around an outer surface of the spindle encoder pulley and an outer surface of the encoder pulley to transmit a rotational force of the spindle encoder pulley to the encoder pulley and in that the clutch member comprises: a clamping clutch installed in front of the spindle encoder pulley to be rotatable about the axial direction of the spindle and axially movable such that the clamping clutch linearly moves forward to come into close contact with a rear end portion of the housing when the clutch drive unit moves forward; and a spindle rotating clutch connected to the clamping clutch behind the spindle encoder pulley to move backward together with the clamping clutch and come into close contact with a front side of the driving member when the clamping clutch is moved backward by the clutch drive unit. a housing fixedly installed on a main body of a machine tool; a spindle having a hollow tube shape and provided inside the housing to be rotatable with respect to the housing; a driving member disposed outside a rear portion of the spindle to be rotatable relative to the spindle; a spindle motor configured to rotate the driving member; a clutch member which is installed on an outer surface of the spindle to be linearly movable in an axial direction with respect to the spindle 20 between the driving member and one end portion of the housing and which is coupled to the driving member or the housing depending on a direction of movement thereof to selectively connect the spindle to one among the driving member and the housing; a clutch drive unit configured to actuate the clutch member; a drawbar which is formed inside the spindle to permit linear movement thereof in an axial direction with respect to the spindle but preclude rotational movement thereof relative to the spindle, such that the drawbar linearly moves in the axial direction with respect to the spindle or moves together with the spindle depending on the spindle restriction conditions set by the clutch member; an encoder configured to measure an amount of rotation of the spindle; and an encoder rotation device connected to the clutch member and the encoder to transmit a rotational force of the clutch member to the encoder when the clutch member rotates together with the spindle, characterized in that the encoder rotation device comprises a spindle encoder pulley coupled to the clutch member and rotating together with the clutch member, an encoder pulley connected to a shaft of the encoder, and a belt wound around an outer surface of the spindle encoder pulley and an outer surface of the encoder pulley to transmit a rotational force of the spindle encoder pulley to the encoder pulley and in that the clutch member comprises: a clamping clutch installed in front of the spindle encoder pulley to be rotatable about the axial direction of the spindle and axially movable such that the clamping clutch linearly moves forward to come into close contact with a rear end portion of the housing when the clutch drive unit moves forward; and a spindle rotating clutch connected to the clamping clutch behind the spindle encoder pulley to move backward together with the clamping clutch and come into close contact with a front side of the driving member when the clamping clutch is moved backward by the clutch drive unit. a clamping clutch installed in front of the spindle encoder pulley to be rotatable about the axial direction of the spindle and axially movable such that the clamping clutch linearly moves forward to come into close contact with a rear end portion of the housing when the clutch drive unit moves forward; and a spindle rotating clutch connected to the clamping clutch behind the spindle encoder pulley to move backward together with the clamping clutch and come into close contact with a front side of the driving member when the clamping clutch is moved backward by the clutch drive unit.