A method is provided for measuring an absolute steering angle of a steering shaft for a vehicle, using a first rotatable body that rotates together with the steering shaft of the vehicle at a predetermined rotation ratio. The method includes obtaining a _M value by measuring a relative rotational angle of the first rotatable body using an angle sensor having a measurement range of . The method also includes obtaining a present value for a frequency i-value of the first rotatable body by comparing the present _M value to a previous _M value. The method also includes obtaining a present value for a absolute steering angle 1 of the steering shaft from a present value for an absolute rotational angle of the first rotatable body by using the _M value and the present i-value.