The company still has registered headquarters in Fukui, but the actual head office is located in Shinjuku, Tokyo.

Santaro Kumagai, the company's founder, began his career as a civil servant in a police department.

His construction career started as a stonemason, crafting religious monuments and performing work for the expanding railway network.

Between 1955 and 1983 the company accounted for more than 10% of all contracts awarded to the fifty-seven members of the Overseas Construction Association of Japan, a figure that outranked the ‘Big Five’ domestic giant construction companies.

Kumagai Gumi took advantage of the situation and sought work overseas, as both as a construction company and a developer, using BOT as project financing, becoming one of the leading proponents of BOT in Southeast Asia.