PURPOSE: To detect the angular speed accurately even during the period when the output of a gyro is not settled by storing the output variation characteristics, appearing in the output of an oscillation gyro immediately after start thereof, in a memory means and reading out the output variation characteristics after starting the gyro and correcting the angular speed.

CONSTITUTION: Upon starting an oscillation gyro 1, a CPU 14 begins operation and counts the time elapsed after starting operation. A decision is then made whether the count is lower than the number of regions prepared for an RAM 15. When the count is higher than the number of regions, the operation is ended otherwise (when the count is higher than the number of regions) a decision is made whether a mobile is stationary currently. If it is stationary, output from the oscillation gyro 1 is written in a data region and the operation is ended otherwise an offset value is read out from the data region before the operation is ended. In this regard, the CPU 14 determines a variation of voltage corresponding to an angular speed component caused by movement based on the difference between the offset value being read out and the output from gyro thus determining a current angular speed from an output data.