Honkan was a general term of government posts which did not belong to the system for shitokan (four classifications of bureaucrats' ranks) of each government official in the ritsuryo system (a system of centralized government based on the ritsuryo code [historical law system]) of Japan.
Chinese ritsuryo system also had a government post called 'honkan' but in this case, it meant all government posts (they were equivalent to shikijikan [a person with an official rank but has no corresponding position] in Japan) which belonged to kanhin (governmental officials classified into nine grades from first honkan to ninth honkan) of over Junior Ninth Rank and honkan in Japan had a completely different definition although the name was derived from Chinese honkan (However, it is said that 'honkan' was also used in the sense of shikijikan in Japan).
Honkan in Japan systemically belonged to some government officials but also constituted Bekkyoku which performed technical official duties apart from shitokan and the kanisoto (the ranks of the bureaucracy system under the ritsuryo system) was provided by Court ranking law. The representative honkan included jiju (Imperial Household Agency staff), naiki (secretary of the Ministry of Central Affairs), and kenmotsu (a auditor Nakatsukasa sho, the Ministry of Civil Affairs), who were belonged to Nakatsukasasho (Ministry of Central Affairs), a judge (in the ritsuryo system) who belonged to Gyobusho (Ministry of Justice) and so on.
Chinese ritsuryo system also had Bekkyoku but had a policy of sanhansei which 'hangan' who controlled Bekkyoku was placed under the command of 'kami' (a director) who controlled government officials and 'suke' who played a part of tsuhan (an official supporting a governor), and was supervised by kenkosei (system to inspect management), however, shitokan and honkan in Japan were not in such a relationship. It was because in Japanese ritsuryo system, each sho (Ministry), shiki (agency), tsukasa (office) and ryo (bureau) had a certain independence, in addition, it is said that it arose since government officials (such as kenmotsu and a judge) which had existed and been independent before the ritsuryo system were forced to be added into jurisdiction of a specific sho with keeping the traditional independence, and as a result, many honkan gathered especially in the Nakatsukasasho which took charge of general affairs within the Imperial Court.