A baseline processing device and method are provided for analyzing signals with uneven distributions of pulses and slow varying baselines. In one embodiment, the device includes an A/D sampling unit for sampling a digital counting signal to obtain sampled data, and a baseline extracting unit for sorting the N sampled data in the sampling sequence by magnitude and for outputting, among the N sample data, one sample data A with a value equal to the mid-value in the N sample data. A phase compensating unit with a width of M, to which a digital signal is input, outputs a sampled data B according to a FIFO sequence, wherein M=N/2. A first subtractor subtracts the sample data A from the sample data B and outputs the result as baseline removed data.