Abstract: Negotiorum gestio which is defined as the legal obligation and quasi-contract in the Civil Code is placed at the end of the Contract Part from the point of exterior system. There are three genres of negotiorum gestio, the legal negotiorum gestio that conforms to the personal will or public order and moral, illegal negotiorum gestio, special negotiorum gestio in the case of emergency. The inadequacy of stipulations can be supplemented by applying the rule concerning agency appointment contract. The interior system is aimed at balancing the values of the private domain not infringed by others and the advocate of mutual help. Based on the principle of autonomy, upholding the public order and moral, promotion of brave act of righteousness, the behavior which is involved in the private domain of others can be justified, appearing in the distribution of right and obligation for each party. The reimbursement of the borne expense of the administrator, debt payments, obligation of compensating the damages to some appropriate extent, duty of care in the management process, obligation of continuing management and giving notice, duty of reporting and handing over are all stipulated, which is reforming the fragmentary negotiorum gestio in the original de lege lata.