A filter state detection device includes a first pressure detection part, a second pressure detection part, and a filter state determination part. The filter state determination part is configured to include an operation part and a storage part. The operation part is configured to apply Fourier transformation to each of values of first and second pressures to obtain first and second spectral intensities and/or phases at a zero frequency and first and second spectral intensities and/or phases at a predetermined frequency and configured to compare the first spectral intensity and/or phase at a zero frequency and the first spectral intensity and/or phase at the predetermined frequency as a first group against the second spectral intensity and/or phase at a zero frequency and the second spectral intensity and/or phase at the predetermined frequency as a second group to determine a state of a filter.