A steering torque detecting device comprises a steering shaft consisting of an input shaft and an output shaft, a torsion bar provided between the input shaft and the output shaft, a torque detecting unit for converting a quantity of torsion produced in the torsion bar into an electric output, an electricity collecting unit comprising slip rings and brushes which takes the electric output and supplies an electric power from an outer power source, bearings for supporting the input and output shaft on the same axial line, and a housing supporting the bearings, a printed wiring board in a circular plate form which is provided at its one surface with a resistance layer and an output electrode radially spaced apart from the resistance layer, the resistance layer and the output electrode constituting a potentiometer, and a slider having a portion extending in the radial direction of the circular printed wiring board so as to have contacting areas with a small width to the resistance layer and the output electrode.