My research interests are discrete optimization and mathematical programming. In the recent five years, I have been working (1) the maximum weight stable set problem on bidirected graphs and (2) discrete convex analysis. In the first theme, I gave polynomial time algorithms for the problem in classes of perfect, claw-free, and chordal bidirected graphs. I also gave polyhedral characterizations of perfectness of bidirected graphs. In discrete convex analysis, I gave circuit axioms of valuated matroids, new characterizations of M-convex functions, proximity theorems of discrete convex functions, and a polynomial time algorithm for minimizing an M-convex function. My most recent interest is an application of discrete convex analysis to the economic models called matching models. I proposed a general matching model and proved the existence of stable outcomes in the model. This implies the existence of stable outcomes in many existing matching models.