An inertial force sensor has a first sensor element, a second sensor element, a first signal processor, a second signal processor, and a power controller. The first sensor element converts a first inertial force to an electric signal, and the second sensor element converts a second inertial force to an electric signal. The first signal processor is connected to the first sensor element, and outputs a first inertial force value. The second signal processor is connected to the second sensor element, and outputs a second inertial force value. The power controller is connected to the first signal processor and the second signal processor, and changes power supplied to the second signal processor based on the first inertial force value.