To examine the freezing and melting behavior of water in partially filled pores of porous silica, we performed X-ray diffraction measurements of water confined inside the cylindrical pores of SBA-15 with a pore radius of 3.9 nm as a function of temperature and pore filling. The freezing temperature increased continuously with increasing pore filling even in the region of capillary condensation. The results are related to the different states of the pore water depending on the degree of pore filling. On the other hand, the melting of the frozen pore water took place at a well-defined temperature of 256 K, independent of the level of pore filling. The X-ray diffraction patterns show that the freezing of the pore water results in formation of ice microcrystals with almost the same structure and size, irrespective of the different states of the pore water.