A construction project is accomplished by the organized production with various and complicated activities. Productivity management for each activity is very important for completing the project successfully. In general, this work productivity is utilized as the index which shows the construction capacity of a construction company and affects to its profit ultimately. So, the improvement of work productivity through the effective field management is an important issue that should always be considered. In case of domestic construction industry, the terminology and concept of productivity seems to be very common, but its meaning is still regarded as ambiguous and inclusive. Specifically, most of researches relating to productivity are performed with an up-to-date keyword. However, the foundation studies such as the identification and analysis of productivity impact factors are actually insufficient. Therefore, this research identified and analyzed productivity loss factors which may occur on construction job sites. Also, it tried to suggest both the causes and solutions for productivity loss with the Delphi technique and reliability analysis. Based upon the research result, it is supposed to improve work productivity by acknowledging and making efforts to avoid potential risks associated with those identified factors early ahead of performing construction projects.