A detecting unit for detecting a torque applied to a rotor according to rotation of the rotor having an input shaft and an output shaft connected with each other by a torsion bar and a detection circuit board connected with the detecting unit are molded with synthetic resin material to form a mold member. The installation of the mold member into a housing, which has a cylinder portion to surround the rotor and a retainer having an opening formed at the peripheral wall of the cylinder portion, is achieved by inserting the mold member into the retainer from the radial direction through the opening of the retainer.