An electric power steering apparatus (1, 64) comprises a housing (10) for supporting a steer shaft (9) for axial slide movement, a speed reduction mechanism (23), and a motion converting mechanism (24, 76). The housing (10) includes a plurality of split housings (36, 37; 36, 37A, 70) connected to each other. The speed reduction mechanism (23) includes an output gear (22) surrounding the steer shaft (9). The motion converting mechanism (24, 76) includes a rotary sleeve (28) surrounding the steer shaft (9) and rotatable integrally with the output gear (22) and converts the rotation of the rotary sleeve (28) into axial movement of the steer shaft (9). The rotary sleeve (28) is rotatably supported by first and second bearings (30, 31) disposed on opposite sides of the output gear (22). The split housings (36, 37; 36, 37A, 70) include main split housings (37, 37A) rotatably supporting an input gear (21) and supporting the first and second bearings (30, 31).