The existence of gravitational waves was predicted by A. Einstein more than 90 years ago, but we have not yet detected them. This is because gravitational waves hardly interact with matter, which, in other words, means that gravitational waves can penetrate any matter in the universe. This fact makes a gravitational wave a very unique means for observation of the universe. By gravitational waves we could see various celestial phenomena which cannot be seen by electromagnetic waves, such as the beginning of the universe down to the Planck time, collision of black holes, and inside a supernova. We call this new astronomy, gravitational wave astronomy. It is expected that gravitational waves will be detected for the first time within several years and then a new window for astronomy will be opened. In this talk, I will briefly explain the significance of gravitational wave astronomy, detection of gravitational waves using a laser interferometer, the current status of large detectors such as LIGO and LCGT. Then I will focus on DECIGO, the Japanese space gravitational wave antenna, which could detect gravitational waves produced during the period of the inflation of the universe, directly measure the acceleration of the expansion of the universe, and reveal the mechanism of formation of supermassive black holes in the center of galaxies. I will also explain our novel techniques "displacement-noise free interferometer" and "juggling interferometer", which could be breakthrough techniques to drastically improve the sensitivity for the 3rd-generation detectors.