An electric linear actuator comprising: a housing; an electric motor mounted on the housing; a speed reduction mechanism for transmitting the rotational power of the electric motor to a ball screw mechanism via a motor shaft with reducing a motor speed; and the ball screw mechanism for converting the rotational motion of the electric motor transmitted via the speed reduction mechanism to an 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 (19, 20) 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 helical screw groove of the nut, adapted to be inserted into the nut via a large number of balls, and supported on the housing axially movably but not rotationally wherein the housing comprises a first housing and a second housing arranged with its end face being abutted against the end face of the first housing, the electric motor being mounted on the first housing and the bores (11 and 12) formed in the first and second housings (2a and 2b) respectively for containing the screw shaft; the speed reduction mechanism comprises an input gear secured on the motor shaft, an intermediate gear (4, 29) mating with the input gear, and an output gear mating with the intermediate gear (4, 29) and secured on the nut; and characterized in that the intermediate gear (4, 29) is rotationally supported via a bearing (23 or 30) on a shaft supported at its opposite ends on the first and second housings (2a, 2b). a housing; an electric motor mounted on the housing; a speed reduction mechanism for transmitting the rotational power of the electric motor to a ball screw mechanism via a motor shaft with reducing a motor speed; and the ball screw mechanism for converting the rotational motion of the electric motor transmitted via the speed reduction mechanism to an 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 (19, 20) 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 helical screw groove of the nut, adapted to be inserted into the nut via a large number of balls, and supported on the housing axially movably but not rotationally wherein the housing comprises a first housing and a second housing arranged with its end face being abutted against the end face of the first housing, the electric motor being mounted on the first housing and the bores (11 and 12) formed in the first and second housings (2a and 2b) respectively for containing the screw shaft; the speed reduction mechanism comprises an input gear secured on the motor shaft, an intermediate gear (4, 29) mating with the input gear, and an output gear mating with the intermediate gear (4, 29) and secured on the nut; and characterized in that the intermediate gear (4, 29) is rotationally supported via a bearing (23 or 30) on a shaft supported at its opposite ends on the first and second housings (2a, 2b).