To provide a signal processing device capable of suitably eliminating noise included in an output signal from a sensor according to the magnitude of the noise.

The signal processing device 1 comprises a filtering means 2 for subtracting a signal having a frequency not lower than a predetermined frequency from an input signal u inputted from a detecting means for detecting the quantity of the movement state of an object, a subtracting means 3 for acquiring a difference signal between the input signal u and a filtered signal S1 outputted from the filtering means 2, a neutral zone reference value calculating means 4 for calculating a neutral zone reference value S5 for defining the width of a neutral zone according to a value of a subtracted signal S2 outputted from the subtracting means 3, a neutral zone processing means 5 for outputting a neutral zone processing signal S6 by processing the subtracted signal S2 according to magnitude resulting from comparison between the subtracted signal S2 and the neutral zone reference value S5, and an adding means 6 for adding the filtered signal S1 and the neutral zone processing signal S6.