The Golgi apparatus is an organelle involved in sorting and trafficking of proteins in the cell. There has been a debate, however, for a long period of time how essential cargo proteins traverse the Golgi apparatus, despite lots of efforts by many researchers. Molecular Membrane Biology Laboratory has developed the world's highest-performance confocal laser scanning microscopic system, which can image directly the nano-scale world of living cells; the temporal and spatial resolution exceeds the long-standing limitation of optical microscopy. By use of the new microscopic system, critical evidence for the mechanism of protein trafficking was provided; that is, not only cisternae mature over time conveying cargo proteins but also dynamic membrane segregation plays a role in the sorting.