An electric linear actuator comprising: a housing; an electric motor mounted on the housing, the electric motor including a shaft (M/S); and a speed reduction mechanism for reducing the rotational speed of the electric motor and transmitting the rotational power of the electric motor to a ball screw mechanism for converting the rotational motion of the electric motor to the 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 rolling bearings (20 and 20) 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 numerous balls, and supported axially movably but not rotationally relative to the housing, wherein the housing comprises a first housing on which the electric motor is mounted and a second housing to be abutted against an end face of the first housing, wherein the first housing is formed with a cylindrical gear containing portion for containing the speed reduction mechanism, the cylindrical gear containing portion encircling the electric motor shaft (M/S) and the speed reduction mechanism, wherein part of an end of the gear containing portion of the first housing extends radially inward to form a bottom portion for covering the speed reduction mechanism, and wherein the bottom portion of the first housing and the second housing are formed with abutment surfaces (21 and 22) respectively for abutting against each other, characterized in that each of the abutment surfaces (21 and 22) respectively of the first and second housings (2a and 2b) is formed to have a circular configuration, and in that the housing is a two-piece housing formed by the first and second housings (2a and 2b). a housing; an electric motor mounted on the housing, the electric motor including a shaft (M/S); and a speed reduction mechanism for reducing the rotational speed of the electric motor and transmitting the rotational power of the electric motor to a ball screw mechanism for converting the rotational motion of the electric motor to the 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 rolling bearings (20 and 20) 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 numerous balls, and supported axially movably but not rotationally relative to the housing, wherein the housing comprises a first housing on which the electric motor is mounted and a second housing to be abutted against an end face of the first housing, wherein the first housing is formed with a cylindrical gear containing portion for containing the speed reduction mechanism, the cylindrical gear containing portion encircling the electric motor shaft (M/S) and the speed reduction mechanism, wherein part of an end of the gear containing portion of the first housing extends radially inward to form a bottom portion for covering the speed reduction mechanism, and wherein the bottom portion of the first housing and the second housing are formed with abutment surfaces (21 and 22) respectively for abutting against each other, characterized in that each of the abutment surfaces (21 and 22) respectively of the first and second housings (2a and 2b) is formed to have a circular configuration, and in that the housing is a two-piece housing formed by the first and second housings (2a and 2b). a nut formed with a helical screw groove on its inner circumference and supported by rolling bearings (20 and 20) 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 numerous balls, and supported axially movably but not rotationally relative to the housing, wherein the housing comprises a first housing on which the electric motor is mounted and a second housing to be abutted against an end face of the first housing, wherein the first housing is formed with a cylindrical gear containing portion for containing the speed reduction mechanism, the cylindrical gear containing portion encircling the electric motor shaft (M/S) and the speed reduction mechanism, wherein part of an end of the gear containing portion of the first housing extends radially inward to form a bottom portion for covering the speed reduction mechanism, and wherein the bottom portion of the first housing and the second housing are formed with abutment surfaces (21 and 22) respectively for abutting against each other, characterized in that each of the abutment surfaces (21 and 22) respectively of the first and second housings (2a and 2b) is formed to have a circular configuration, and in that the housing is a two-piece housing formed by the first and second housings (2a and 2b).