His ambition turned to medicine as a number of children died in his village due to infectious diseases and malnutrition. In 1921 he entered Kyoto Imperial University's School of Medicine. In 1940 he earned a PhD in medicine, and joined the faculty of medicine at Kyoto University. During the Japanese invasion of China, he was appointed as a military doctor. Then he became a professor at the University Medical Harupin, China. After the war he returned to Japan to establish Shirota Research Centre in 1939. In 1950 he started Yakult company. In 1955 he moved its company headquarters to Tokyo.