This power steering apparatus comprises: a steering shaft 10 which includes an input shaft 11, an intermediate shaft 13 connected to the input shaft via a first torsion bar 12, and an output shaft 15connected to an intermediate shaft via a second torsion bar 14; a hollow motor 30 which applies rotation force to the intermediate shaft; and a control device 60 which is provided with a microcomputer. The control device is provided with: an output-shaft rotational angle estimation unit 63 which estimates an output-shaft rotational angle theta g, on the basis of signals of an input-shaft rotational angle theta h and an intermediate-shaft rotational angle theta m, a torsion spring constant g1 of the first torsion bar, and a torsion spring constant g2 of the second torsion bar; and a motor drivecontrol unit 69 which controls the hollow motor on the basis of the output-shaft rotational angle.