A plagiarism detection program causing a computer to perform processing of: converting a target document into a first numerical matrix; generating a first conversion matrix by performing discrete Fourier transform on the first numerical matrix; generating a detection matrix which is used for plagiarism detection by masking a upper row of the first conversion matrix with 0; converting a query document into a second numerical matrix; generating a second conversion matrix by performing the discrete Fourier transform on the second numerical matrix; creating an element product matrix by multiplying each element of the second conversion matrix; and acquiring a vector relating to match between the target document and the query document by performing inverse discrete Fourier transform after elements of the created element product matrix are summed.