PURPOSE: To simplify the structure of a motor-operated power steering device by obtaining a clutch to be automatically in with such a constitution that when an input shaft is rotated and its rotational torque exceeds the set torque of a torsion bar, a coil spring is enlarged in its diameter through a pressing part.

CONSTITUTION: A steering handle 30 is rotatively operated so as to rotate an input shaft 11, and when its steering force exceeds the set torque of a torsion bar 24, the torsion bar 24 is largely twisted so that a clearance A in the rotational direction disappears, and a square hole 21 becomes engaged with a rectangular shaft 22 so that the steering force is transmitted to a wheel from the input shaft 11 through the rectangular shaft 22, an output shaft 12, a pinion shaft 33, a pinion 32 and a rack 37. In addition, a fork 19 rotated together with the input shaft 11 pushed an engagement piece located at the front side in the rotational direction of the fork 19 in the peripheral direction, and a coil spring is thereby enlarged in its diameter and pressed to an outer wheel 13 so as to obtain a clutch connecting state. In this state, the driving force of a motor 35 can be transmitted to the output shaft 12 as steering auxiliary force from the outer wheel 13 through the coil spring 16.