Although construction schedule is often delayed due to numerous reasons, the management efforts of preventing and managing events that cause such delays tend to be diminished as each participant has different perception on the level of their importance. After listing 23 major factors causing schedule delays in concrete structural works of apartment projects from literature review and expert interviews, the differences of the perception have been analyzed by using the AHP. Five factors causing construction schedule delay the most were revealed from the analysis with a data of 46 survey responds, namely ‘Inaccurate master schedule prepared by owner’, ‘Accident’, ‘Labor union issues related to construction equipment’, ‘Errors and omissions on estimation’, and ‘Inappropriate plan of temporary work’. It was also found that main contractors and subcontractors have completely different thoughts on the importance of several factors, such as ‘Labor shortage of subcontractors’, ‘Different management style on labor allocation between contractors and subcontractors’, and ‘CP plan without consideration of works order’. Moreover, the factor of ‘Inaccurate master schedule prepared by owner’is ranked as the second by both participants. It could be therefore clearly said that most industry personnel believes schedule is delayed due to other’s faults, which diminishes management efforts of preventing and/or managing schedule delays. It will be a great interest for all the parties being involved in a construction to understand and minimize the differences for better schedule management.