A warm water porcupine puffer Cyclichthys spilostylus was collected in Ryotsu Bay, Sado Island, Niigata Prefecture, Japan, which is the northernmost record of this species. The coast waters of the Sea of Japan becoming gradually warmer, warm water marine animals including this species may extend their habitat to the north. The toxicity still unknown, C. spilostylus ought not to be eaten if collected.