A clamping device for releasably holding a tool holder shank, the clamping device comprising: - a housing; - a spindle rotatably mounted inside the housing and having a front end, a rear end and a bore which intersects the front end and extends rearwardly therefrom, wherein a mounting portion for receiving the tool holder shank is provided at a front end of the bore; - a drawbar slidably mounted inside the bore so as to be reciprocally moveable in the bore along a longitudinal axis thereof between an advanced releasing position and a retracted locking position; - engagement members arranged around the drawbar at a front end thereof, wherein the engagement members, under the effect of a movement of the drawbar from the advanced releasing position to the retracted locking position, are moveable from a first position, in which the engagement members allow the tool holder shank to move into and out of said mounting portion of the bore, to a second position, in which the engagement members are in locking engagement with the tool holder shank and keep it secured to the spindle, characterized in that the clamping device further comprises: - a hydraulically operated actuating sleeve arranged inside the housing, wherein the actuating sleeve is arranged around a peripheral wall of the spindle and slidably mounted to this peripheral wall so as to be axially moveable in relation to the spindle; - a motion transferring mechanism arranged inside the housing, wherein the motion transferring mechanism is mounted to the spindle and configured to transfer an axial movement of the actuating sleeve in a first axial direction in relation to the spindle into a movement of the drawbar from the advanced releasing position to the retracted locking position; and - a hydraulic cylinder arrangement arranged inside the housing and configured to move the actuating sleeve axially in relation to the spindle, wherein the hydraulic cylinder arrangement comprises a cylinder casing, which is concentric with the actuating sleeve and which is fixed to spindle on the outside thereof so as to be rotatable in relation to the housing together with the spindle, and an annular piston head, which is fixed to or fixedly connected to the actuating sleeve, the piston head being slidably received in an annular space inside the cylinder casing and configured to divide this space into an annular first hydraulic chamber on a first side of the piston head and an annular second hydraulic chamber on an opposite second side of the piston head, wherein the actuating sleeve is moveable together with the piston head in said first axial direction by feeding of hydraulic fluid into the first hydraulic chamber and in an opposite second axial direction by feeding of hydraulic fluid into the second hydraulic chamber. - a housing; - a spindle rotatably mounted inside the housing and having a front end, a rear end and a bore which intersects the front end and extends rearwardly therefrom, wherein a mounting portion for receiving the tool holder shank is provided at a front end of the bore; - a drawbar slidably mounted inside the bore so as to be reciprocally moveable in the bore along a longitudinal axis thereof between an advanced releasing position and a retracted locking position; - engagement members arranged around the drawbar at a front end thereof, wherein the engagement members, under the effect of a movement of the drawbar from the advanced releasing position to the retracted locking position, are moveable from a first position, in which the engagement members allow the tool holder shank to move into and out of said mounting portion of the bore, to a second position, in which the engagement members are in locking engagement with the tool holder shank and keep it secured to the spindle, - a hydraulically operated actuating sleeve arranged inside the housing, wherein the actuating sleeve is arranged around a peripheral wall of the spindle and slidably mounted to this peripheral wall so as to be axially moveable in relation to the spindle; - a motion transferring mechanism arranged inside the housing, wherein the motion transferring mechanism is mounted to the spindle and configured to transfer an axial movement of the actuating sleeve in a first axial direction in relation to the spindle into a movement of the drawbar from the advanced releasing position to the retracted locking position; and - a hydraulic cylinder arrangement arranged inside the housing and configured to move the actuating sleeve axially in relation to the spindle, wherein the hydraulic cylinder arrangement comprises a cylinder casing, which is concentric with the actuating sleeve and which is fixed to spindle on the outside thereof so as to be rotatable in relation to the housing together with the spindle, and an annular piston head, which is fixed to or fixedly connected to the actuating sleeve, the piston head being slidably received in an annular space inside the cylinder casing and configured to divide this space into an annular first hydraulic chamber on a first side of the piston head and an annular second hydraulic chamber on an opposite second side of the piston head, wherein the actuating sleeve is moveable together with the piston head in said first axial direction by feeding of hydraulic fluid into the first hydraulic chamber and in an opposite second axial direction by feeding of hydraulic fluid into the second hydraulic chamber.