Freezing phenomena in confined space were explored, looking at three of possible major factors: i) strength of pore wall potential (compressing effect), ii) geometrical shape of pore (geometrical hindrance), and iii) equilibrium vapor-phase pressure (tensile effect). Each effect was clarified quantitatively by molecular simulation technique suitable for each purpose. A perspective of the whole phase diagram for LJ fluid in nanopores are discussed from the viewpoint of "the pressure felt by the confined fluid," which proves its usefulness in understanding and estimating freezing behavior in nanopores.