An operation parameter detecting apparatus for a vehicle is provided to obtain a pedaling torque value, an angle of a central shaft with a magnetic ring, a corresponded rotating speed and a corresponded pedaling power, respectively by measuring an electromagnetic force of a coil induced by a magnetic variation due to a deformation of a covered magnetic sleeve linked to a central shaft, a voltage output from at least a Hall corresponded to a magnetic flux density of which the distribution in a 1, 2 or 3 dimensional space is partly a monotonic increasing or decreasing function in an area with the same polarity, and at calculation relative to the time.