To constitute a compact unit type motor-driven power steering gear applicable in a wide range including a manual steering mechanism, and excellent in interchangeability.

In this motor-driven power steering gear 1, a pinion shaft 4 of a steering mechanism is constituted of an input shaft 8 for fixing it to a steering side and an output shaft 11 formed with a pinion 10, a motor output shaft of an electric motor 2 is arranged to be substantially orthogonal to the output shaft, a power transmission part 6 is connected to an input side of the pinion in the output shaft, a torque detecting part 5, the motor and the power transmission part are constituted integrally onto the input and output shafts, the input and output shafts are projected from upper and under sides of a housing 3 to form a unit, and the housing is attached detachably to a rack shaft case 31 for holding a rack 9.