I study the mechanism of the Active Galactic Nucleus (AGN) jets using supercomputer simulations. AGN jets are relativistically-accelerated plasma outflows from AGNs, the central engines in the center of galaxies. The driving mechanism of the AGN jets has been one of the biggest enigmas in modern astronomy. The most promising possibility is that it should be related to a supermassive black hole in the AGN and magnetic fields surrounding it. Bearing this in mind, I investigate how to extract information on the magnetic fields from linear and circular polarization images around the black hole.