One inertial sensor detects an acceleration in a driving direction as well as an angular rate about one axis and an acceleration in a detecting direction at the same time. A driving-direction acceleration detecting unit is provided to members vibrating in mass members on the left and right via an elastic body. In this manner, when an acceleration is applied in the driving direction, the mass members on the left and right normally vibrated with a same amplitude and in opposite phases have displacement amounts in a same phase, and the driving-direction acceleration detecting unit detects the displacement amounts in the same phase as a capacitance change, thereby detecting the acceleration in the driving direction.