Abstract: An object of the present invention is to provide a method of a practical level for performing sensor fusion of multiple vibration sensors such as a seismometer, and in an example, to extend a dynamic range of a high-sensitivity geophone by sensor fusion of the high-sensitivity geophone and a low-sensitivity acceleration geophone. A state related to the high-sensitivity geophone is estimated by capturing, in a Kalman filter, an acceleration record from the low-sensitivity acceleration geophone and a velocity record, or a displacement record, and an acceleration record of the high-sensitivity geophone, and estimating and calculating them as the linear Kalman filter problem with a control input. The high-sensitivity geophone is an actual device, but the state can be estimated using a sensor value of the low-sensitivity acceleration geophone even when the record is saturated. This extends the dynamic range of the high-sensitivity geophone.