Today, as the use of computers, communication, and automation equipment increases, the demand for development of software used in hardware is also increasing, and software development contracts are also frequently signed. In the case of software development contracts, the development requirements or the details of what developers have to do at the time of signing the contract are often not specifically determined in the contract, resulting in a lot of disputes regarding “Whether the work has been completed” or defect liability. Therefore, in this study I examined the content of an obligation to complete work and defect liability and the relationship between them so that it can be used as a reference in resolving or preventing wasteful disputes at software development sites.
 In the case of software development contracts, as it is difficult to expect the delivery of a complete product without any defects, the criteria for determining the completion of work is somewhat eased compared to ordinary contracts for work, so the ordering party cannot deny “work completion” due to minor defects. Therefore, if there is a minor defect in the software delivered by the developer after completing the development of it, the ordering party must acknowledge the completion of the work and pay compensation corresponding to the completion of the work, and the ordering party can only claim defect liability for such minor defect against the developer. In other words, the wider the scope of defects to be resolved by the defect liability, the narrower the scope of defects recognized as the incompletion of work, so it can be said that the obligation to complete work and the defect liability have a complementary relationship. In addition, even if the work as a whole is incomplete, in certain cases, remuneration may be paid for the completed part.
 If this research results can be referenced for the software development contract practice, consumptive disputes arising from unjust denial of the completion of work due to minor defects can be prevented, and disputes that have occurred can be reasonably adjusted. However, in order to more actively protect small software development companies, it is necessary to clarify the obligation of the contracting party through legislation. Therefore, in Chapter 4 of this study, I made legislative suggestions.