The invention discloses a starting separation device of an internal combustion engine. The starting separation device comprises a box body. A diesel engine connecting shaft and a starting shaft are mounted in the box body, the diesel engine connecting shaft and the starting shaft are parallel to each other, the diesel engine connecting shaft and the starting shaft are fixedly provided with a driving gear and a driven gear respectively, and the driving gear and the driven gear are in meshed transmission. The front end of the starting shaft is sleeved with a reset spring. The starting separation device of the internal combustion engine is simple in structure and convenient to manufacture, and a diesel engine can be manually started simply and conveniently in a labor-saving mode.