This is probably a species of orb weaver spider but I have not seen such a display of colors on any other spider. A display of colors is often a warning to predators that says, “If you try to eat me, you will be sorry”, because the colors often mean !poisonous!. (This is true, for example, of Monarch Butterflies, which feed on milkweed as caterpillars and milkweed contains bitter, poisonous glycosides.) Here, this spider is feeding on some small insect. The doubt about the spider’s identity arises because the picture was taken in Japan in a park that had an uncountable number of orb-weaver type webs, each 2-3 feet in diameter.