In order to conduct construction projects effectively, the work delay factors would be managed by planned construction schedules. As construction works are delayed ceaselessly, the solution is to select and manage the key factors which delay the work ceaselessly. The subjects of this study were an apartment houses of reinforced concrete structure. Hidden work delay factor were extracted, the surveys were conducted and occurrence, severity and detection of each factor were analyzed. With this result, final orders of priority were fixed and key management factors were deducted and presented.