Gravitational waves are ripples of space-time predicted by Albert Einstein almost 100 years ago. In 2015, the first direct detection of the gravitational waves was achieved. The source was a merger of two black holes. In 2017, the first direct detection of gravitational waves and electromagnetic waves was achieved. The source was a merger of two neutron stars. In this talk, I would like to present what these scientific achievements brought us and what the prospect is.