Japanese pepper, Zanthoxylum piperitum, is native to Japan and has four famous varieties: Asakura, Takahara, Budou, and Arima, named after their production area or morphology. Restriction-site associated DNA sequencing (RAD-Seq) was used to analyse 93 accessions from various areas, including these four varieties. The analysis of the single nucleotide variants was used to classify the plants into eight groups: each of the Asakura and Arima varieties has two groups, each of the Takahara and Budou varieties has one group, and two additional groups are present. In one group of the Asakura varieties and two groups of the Arima varieties, the plants were present in agricultural fields and mountains, representing the early stage of domestication of the Japanese pepper. The second group of the Asakura varieties was of genetically close plants present in various areas, which represents the second stage of domestication of this plant because, after early domestication, genetically related varieties of excellent traits spread to the periphery. These results demonstrate that the domestication of the Japanese pepper is ongoing. In addition, this study shows that spineless plants are polyphyletic, despite the spineless variety being considered a subspecies of the Japanese pepper.