There is provided an electromagnetic wave signal processor configured to process an input pulse signal corresponding to an electromagnetic wave, comprising a signal processing unit including: a peak detecting circuit to detect peak values of each amplitude of the input pulse signal; an AD converter to convert the peak values into digital signals; a memory device comprising memory cells each having an address assigned in accordance with each of values capable of being taken by the digital signals of the peak values, and being able to have any one of a plurality of internal states representing detection frequencies of the peak values; and a writing circuit to change the internal state in the memory cell that has the address corresponding to the value of each digital signal converted by the AD converter, so as to increment the detection frequency represented by the internal state.