To improve a variation in the detection of a crank pulser due to a variation in the accuracy of distances between reluctors.
The reluctors 10 are disposed on the peripheral surface of a rotating body 8 such as a rotor yoke, and a sensor 1 detects the reluctors 10 and outputs pulse signals. A stage period calculation part 66 calculates the period of the pulse signals PLS. A dividing part 67 calibrates the period of the pulse signals with calibration values. The calibrated period is used to calculate the rotational variation values of the rotating body 8. The calculation part 61 of a calibration value determination device outputs actually measured values indicating the intervals between the selected reluctors 10 based on intervals between the pulse signals corresponding to the pre-selected reluctors 10. A reference value storage part 63 outputs the reference values of disposed intervals between the reluctors 10 based on the rotational speed of the rotating body 8. The dividing part 64 calculates the values of the ratio of the actually measured values to the reference value and calculates the calibration values by the dividing part 67 before outputting.
Michito Hiraki
Sanji Tanabe