Inertial sensor and combined sensor therewith

An inertial sensor is provided which includes a self-diagnosis circuit which applies an AC-bias signal voltage ahead of a synchronous demodulator, and thereby, supplies a diagnostic signal for detecting an abnormality in at least one of a detecting element and a detection circuit. This inertial sensor is capable of actively diagnosing whether or not there is an abnormality in the sensor itself, only by monitoring whether a predetermined DC offset signal is obtained from a sensor output terminal of the inertial sensor.