Even though he was living in a closed society, Katsu became an expert in foreign affairs and strongly supported the adoption of scientific and technical knowledge from the West.
當時他是主張「開國論」最有名望的人，曾學過蘭學（指有關荷蘭的航海、天文、工業等的學問，有如當年的現代科學），思想相當開明進步。