My research field is algebraic analysis and micro-local analysis of partial differential equations. The view point of micro-local analysis (with cohomology) is a new important point of view in analysis introduced by Mikio Sato in the early 1970s. Thinking from a micro-local point of view helps us to well understand a number of mathematical phenomena (at least for PDE) and to find a simple hidden principle behind them. Even for some classical facts (scattered as well known results) we can sometimes find a new unified way of understanding from a micro-local or algebro-analytic viewpoint.