Hiroshi Enatsu (12 September 1922 – 4 August 2019) was a Japanese theoretical physicist who contributed to a relativistic Hamiltonian formalism in quantum field theory.

in a relativistic Hamiltonian formalism is equivalent to that in the conventional non-relativistic Hamiltonian formalism of quantum field theory, where

is the Dirac delta function, with the aid of the relation

Miyakonojō is a town within the territory of the former Satsuma Domain, and it was rather natural for Enatsu to receive an education in Kagoshima.

So, he spent in Kagoshima for secondary education and junior college.

In the last year of junior college, Hideki Yukawa made a lecture on meson theory at Kagoshima.

He studied on meson theory under Yukawa in undergraduate course.

He received Bachelor of Science from Kyoto Imperial University in 1944.

Enatsu was an assistant under Yukawa at Kyoto University[4][5] from 1946 to 1957.

Enatsu was a research assistant at Columbia University [6] in New York City from 1952 to 1953.

Enatsu was a visiting member of the Institute for Theoretical Physics in Copenhagen[7][8] from 1955 to 1956.

During his stay in Copenhagen, he could ask some questions to Bohr almost every week.

From 1971 to 1972, he was also the dean of faculty of science and engineering at Ritsumeikan University.

In 1997. he received the 3rd class of the Order of the Sacred Treasure.