What Determines the Coronal Heating in the Photosphere Y. Katsukawa (Univ. of Tokyo / National Astronomical Observatory of Japan) and S. Tsuneta Observations of the solar corona with Yohkoh/SXT, SOHO/EIT and TRACE have revealed that individual loops of active region corona have their own temperatures from 1 MK to 5 MK. The most significant difference between hot (2 - 5 MK) SXT loops and cool (1 - 2 MK) EUV ones is that heat input to maintain the hot loops is about one order of magnitude larger than that for the cool loops. We investigate the photospheric magnetic signature for the hot and cool loops with the Advanced Stokes Polarimeter (ASP) to clarify what makes such a large difference in the heat input. Footpoints of both loops have magnetic fields whose strength is 1.2 - 1.3 kG and the orientation is almost vertical to the surface. A significant difference is discovered in the magnetic filling factor, which is defined by the fraction of the pixel filled with a magnetized atmosphere. The footpoints of the hot loops have significantly lower filling factor than the footpoints of the cool loops. If we interpret the lower filing factor as multiple granular magnetic elements in an ASP pixel, those elemental magnetic footpoints combined with photospheric motion would provide enhanced coronal heating, leading to the hot loops.