An array of recent astrophysical observations show us two unresolved mysteries of cosmology; the accelerating expansion of the universe and the existence of dark matter. In order to realize the cosmic acceleration in General relativity, an exotic form of energy, now called dark energy, should be dominated in the present universe. Another unknown content of the universe is dark matter. Dark matter dominates the dynamics of the universe and plays an important role of formation of rich structure of the universe. Here, we summarize some evidences of the accelerating expansion of the universe and the existence of dark matter. we then introduce the gravitational lensing as a tool to reveal mysterious dark components in the universe.