Shoichiro Irimajiri (入交 昭一郎, Irimajiri Shōichirō, born on January 3, 1940 in Kobe, Japan) is a Japanese engineer and businessman.
He earned an aeronautical engineering degree from the University of Tokyo and worked for Honda Motor Co., Ltd. for 20 years, overseeing the introduction of its CBX motorcycle, design of their F1 racing engines for the RA273 as well as being the president of Honda of America Inc. He resigned in 1992 due to a heart problem, and started a Chinese traditional treatment to restore his condition.
During this time, it was said that General Motors recruited Irimajiri for a senior executive position at the company, in light of his success at Honda. While he declined that position and accepted a spot as an outside director, if Irimajiri had accepted the offer, he would have been the first Japanese-born automotive executive of an American automobile manufacturer.
After his recovery, his friend Hayao Nakayama, then president of Sega Enterprises, asked him to become vice president of the company. He became president of Sega in 1998, where he laid an ambitious plan using the Dreamcast to restore Sega's lost market share and prestige which took a severe downfall following the flawed launch of the Sega Saturn as well as the Sega 32X. After Sega reported its third consecutive loss, Irimajiri resigned and Isao Okawa took his place.
He was last a chairman of Asahi Tec, a Japanese manufacturer of aluminum parts and castings for automobiles, owned by Ripplewood Holdings.