European Space Agency’s Gaia mission has made the 2nd data release (Gaia DR2) on 25th April 2018. Gaia DR2 provides position, parallax and proper motions for more than one billion stars with unprecedented accuracy and radial velocity for about 7 million bright stars. In this talk, I will summarise our Galactic dynamics studies with Gaia DR2. First, I will show that for the first time Gaia DR2 has revealed the velocity sub-structures of the Galactic stellar disk in the large range of radii, 5<Rgal<12 kpc. We found many diagonal ridges in the Rgal vs. Vrot map. We have detected also radial wave-like oscillations of the peak of the vertical velocity distribution. These features indicate that the Galactic disk are heavily perturbed recently. Although it is considered that these features are induced by the interaction with the Sagittarius dwarf, we discuss that to explain the radial and rotational velocity structures seen in Gaia DR2, winding transient spiral arm structures that is commonly seen in N-body simulations of disk galaxies are also necessary. Second, I will talk about our search for dwarf galaxies in Fermi-LAT extended unassociated source fields, and discuss implications for annihilating dark matter. Finally, I will talk about the prospect of the next Gaia data releases and the future astrometry missions, including Small-JASMINE and Gaia NIR.