An electric linear actuator comprising: a housing ; an electric motor mounted on the housing ; a speed reduction mechanism for reducing rotational speed of the electric motor via a motor shaft ; and a ball screw mechanism for converting rotational motion of the electric motor transmitted via the speed reduction mechanism to axial linear motion of a driving shaft ; the ball screw mechanism comprising a nut formed with a helical screw groove on its inner circumference and supported by bearings mounted on the housing rotationally but axially immovably, and a screw shaft coaxially integrated with the driving shaft , formed with helical screw groove on its outer circumference corresponding to the helical screw groove of the nut , inserted into the nut via a large number of balls , and supported on the housing axially movably but not rotationally, and wherein a tapering chamfered portion is formed on the end of the nut , and characterized in : that a sleeve is secured on the housing for preventing rotation of the screw shaft relative to the housing and formed with at least one axially extending recessed groove on the inner circumference of the sleeve ; that at least one guide pin mounted on the end of the screw shaft is engaged with the recessed groove ; and that a blind bore of the housing is formed with flat surfaces corresponding to flat portions of the sleeve , wherein the engagement of the flat surfaces and the flat portions prevent rotation of the sleeve relative to the housing . a housing ; an electric motor mounted on the housing ; a speed reduction mechanism for reducing rotational speed of the electric motor via a motor shaft ; and a ball screw mechanism for converting rotational motion of the electric motor transmitted via the speed reduction mechanism to axial linear motion of a driving shaft ; the ball screw mechanism comprising a nut formed with a helical screw groove on its inner circumference and supported by bearings mounted on the housing rotationally but axially immovably, and a screw shaft coaxially integrated with the driving shaft , formed with helical screw groove on its outer circumference corresponding to the helical screw groove of the nut , inserted into the nut via a large number of balls , and supported on the housing axially movably but not rotationally, and wherein a tapering chamfered portion is formed on the end of the nut , and characterized in : that a sleeve is secured on the housing for preventing rotation of the screw shaft relative to the housing and formed with at least one axially extending recessed groove on the inner circumference of the sleeve ; that at least one guide pin mounted on the end of the screw shaft is engaged with the recessed groove ; and that a blind bore of the housing is formed with flat surfaces corresponding to flat portions of the sleeve , wherein the engagement of the flat surfaces and the flat portions prevent rotation of the sleeve relative to the housing . that a sleeve is secured on the housing for preventing rotation of the screw shaft relative to the housing and formed with at least one axially extending recessed groove on the inner circumference of the sleeve ; that at least one guide pin mounted on the end of the screw shaft is engaged with the recessed groove ; and that a blind bore of the housing is formed with flat surfaces corresponding to flat portions of the sleeve , wherein the engagement of the flat surfaces and the flat portions prevent rotation of the sleeve relative to the housing . <EOS>