Photoresponsive functions of rhodopsin (Rh) in visual cells of vertebrates and bacteriorhodopsin (bR), a photo-driven proton pump in Halobacteria, are reviewed. In both systems, photoisomerization of retinal moieties attached to opsin takes place very fast and this local change in conformation results in the change in conformation of Rh and bR. The photosignals are finally transformed into electrochemical potentials across the membranes. In the visual cells, successive amplifications of the initial photosignals take place in a sophisticated way, which has not been fully understood. In the course of the amplifications, change in physical properties such as conformation and phase seems to play an important roll. In order to achieve highly efficient photoresponsiveness in artificial systems, use of such changes in physical properties as a way of amplification may be highly appreciated. Artificial photoresponsive systems reported recently are discussed in relation to photoresponsiveness in nature.