To realize a structure that enables sufficient reliability in a measurement value at the time of normal operation and quick, proper countermeasures at the time of emergency when an axial load applied on a spindle of a machine tool is measured.

Signal transmission circuits 15a and 15b in parallel with each other are provided for deriving a processing signal obtained by performing processing on an output signal of a sensor by a computing unit 14. One signal transmission circuit 15a is provided with a low-pass filter 16a having a lower cut-off frequency, and the other signal transmission circuit 15b is provided with a low-pass filter 16b having a higher cut-off frequency. At the time of normal operation, a first processing signal passing the one signal transmission circuit 15a is used to execute control. At the occurrence of a failure, a second processing signal passing the other signal transmission circuit 15b is used to execute control or take countermeasures.