Cosmology provides us a unique arena where gravitation and quantum physics meet each other. It is also a unique probe of ultra-high energy physics beyond energies which can be achieved at colliders. I have been working on several aspects of cosmology, e.g., statistical non-Gaussianities of CMB primordial perturbation, calculations of loop corrections to correlation functions of inflationary perturbations, dark energy phenomenology, modifying gravity, and so on.