To provide an inertial sensor and a method for reducing its calculation error in which a calculation error due to output change generated by temperature variations can be reduced comparatively simply and accurately without requiring a complicated means even in the initial use in which temperature characteristics are not learned, or even when ambient temperature to be used is different from before.

An inertial sensor at least includes: a sensor element 51 which senses the inertia; a signal processing circuit; and a memory 58. In the memory 58, memory data is stored which is for estimating characteristics of this inertial sensor. An angular velocity sensor and an acceleration sensor are included in a range of the inertial sensor.