The invention provides a method to correct an offset value accurately even in the case of having an individual difference. The method comprises determining whether the absolute value of a temperature difference between a measured temperature by a temperature sensor and a reference temperature exceeds a prescribed value or not (step S2-stepS4). It is determined whether a body stands still or not on the basis of an output value outputted from an acceleration sensor, when the temperature difference exceeds the prescribed value (step S6-stepS11). It is determined whether the body is on a horizontal plane or not on the basis of the output value outputted from the acceleration sensor, when it is determined that the body stands still (step S12-stepS15). When it is determined that the body is on the horizontal plane, a new offset value corresponding to the output value outputted from the acceleration sensor is stored in an offset value storage means, and the measured temperature is stored in the offset value storage means as a new reference temperature (step S16). |