Solar power sail is a deep space probe to be powered by hybrid propulsion of solar photon acceleration and ion engines to explore outer planetary region of the Solar System without relying on nuclear technology. The Japan Aerospace Exploration Agency (JAXA) launched the world's first deep space solar sail demonstration spacecraft "IKAROS" (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) on May 21, 2010. IKAROS succeeded in deploying a 20m-span solar sail on June 9 and demonstrated several key technologies for solar sail utilizing the deep space flight environment. JAXA is currently studying an outer solar system exploration mission using the demonstrated solar power sail technology. The mission plans to fly for Jupiter, where the spacecraft drops a tiny Jovian probe and performs a swing-by for a Trojan asteroid. Current scenario consists of the rendezvous with one of the Trojan asteroids that are at the Lagrange points L4/L5 associated with Sun-Jupiter system. About as large as 50m sail should be deployed for this mission according to preliminary mission analysis and related research is intensively being carried out in JAXA. JAXA plans to initiate the project in a few years and looks at the launch around 2020.