A processing device that processes detection strengths detected at a first detection position and a second detection position by a detector for detecting detection targets generated from a plurality of sources, includes a two-dimensionalization unit converting detection strengths a pair of sources into a two-dimensional distribution of coordinate points in which the detection strength for one source is represented by an X-axis value, and the detection strength for the other source is represented by a Y-axis value; a demarcation unit demarcating in the two-dimensional distribution of coordinate points, a predetermined region including a mixed region in which coordinate points relating to the first detection position and coordinate points relating to the second detection position are mixed; and a replacement unit replacing the two-dimensional distribution of coordinate points in a demarcated region that has been demarcated, with a two-dimensional distribution of coordinate points relating to another pair of sources.