Naisogata was one of the legal institutions set up in the early stage of the Muromachi bakufu (Japanese feudal government headed by a shogun). It is presumed that Morofusa NAKAJO, a member of Bakufu hyojoshu (an organization of bakufu employing the council system), served as its chief in Jowa era in the period of Northern and Southern courts (Japan) (late 1340's).
During the period of the Kamakura bakufu, direct appeal systems called Naiso and Soji existed. The former was one by which people were allowed to appeal directly to Shikken (regent) or Rokuhara Tandai (an administrative and judicial agency in Rokuhara, Kyoto) and the latter was one by which people were allowed to directly appeal to bakufu in case their appeals were dismissed by Hyojoshu/Hikitsukeshu (coadjustor of the High Court)/Ossobugyo (temporary positions in charge of retrials and accepting appeals in Kamakura bakufu). Naisogata is considered to be the successor of the above systems and people were allowed to appeal to Naisogata in cases where their appeals were dismissed, jurisdiction of legal institutions was not clear or the trial was prolonged. Although Naisogata didn't make any rulings by itself, it was given to the authority to investigate, deliberate, and order a proper legal institution to deliberate the case in question.
It is considered that Naisogata declined and was eventually abolished in the wake of the collapse of bakufu's administrative organization caused by the Kanno Disturbance and it didn't exist in the era of Yoshimitsu ASHIKAGA.