a processor configured to

calculate an approximate line approximating a temporal change of an input data sequence being a sequence of data at time points of a predetermined first number, the time points of the first number being arranged in succession with a predetermined time interval, the input data sequence being inputted from outside;

extrapolate the approximate line to a head or a tail of the input data sequence and to generate a virtual data sequence being a sequence of data representing values on the extrapolated approximate line at time points of a predetermined second number, the time points of the second number being arranged in succession with the time interval, and including a time point being adjacent to the input data sequence;

generate a processed data sequence being a data sequence in which the virtual data sequence is connected to the input data sequence on a side where the approximate line of the input data sequence is extrapolated;

operate as an infinite impulse response (IIR) filter to-process a data sequence that is inputted and to output a data sequence in which a low frequency component is reduced as compared with the data sequence that is inputted, the low frequency component being a component varying at a low frequency;

input data included in the processed data sequence to the IIR filter sequentially; and

output the data sequence outputted from the IIR filter to the outside.