Change orders under construction takes place when a wrong design document is drawn up, when an orderer does not consider preview procedure of compatibility or completeness of design document and when there are differences between site conditions and drawing. Although detailed procedure of change order is established, problems that happened by not observing change order treatment period cause a lot of ripple effects in the side of time and economy under construction. If change order is not carried out during the proper time, payment is delayed. It makes enterprise activity difficult by deteriorating cash flow of contractors and subcontractors and has a negative effect on the whole business by delaying decision-making. To analyze an effect followed by change order delay of public apartment construction, the study analyzed the amount of change order, the amount of material interlocking, delay factors of change order, accumulated status of uncollected the balance by each month, and frequency and delay of change order through survey and consulting with experts with ten fields of public apartments in the metropolitan area, and proposes their measures and how to construct a quick business treatment system.