COAXIAL TYPE ELECTRIC POWER STEERING DEVICE

PROBLEM TO BE SOLVED: To provide a coaxial type electric power steering device capable of increasing assist force by changing a reduction ratio when a steering effort of a driver exceeds predetermined torque. SOLUTION: The coaxial type electric power steering device is provided with a steering shaft 1 steering wheels, an electric motor 3 applying thrust to the steering shaft 1 via a first or second ball screw mechanism 19 or 18, a first rotation transmitting path transmitting rotation from a rotary shaft 6 of the electric motor 3 to the first ball screw mechanism 19 via a first speed reducing mechanism 30, a first rotation transmitting element 25, a second rotation transmitting element 27 capable of coupling and separating to the first rotation transmitting element 25 and a second speed reducing mechanism 38, a second rotation transmitting path transmitting rotation from the rotary shaft 6 of the electric motor 3 to the second ball screw mechanism 18 via a third rotation transmitting element 21 holding a planetary element 34 of the first speed reducing mechanism 30, and an electromagnetic clutch 23 changing between the first rotation transmitting path and the second rotation transmitting path. Reduction ratios in the first rotation transmitting path and the second transmitting path are differentiated.