The aim of this study is to improve quality system through mutual understanding for the opinion gap among interested parties such as owner, designer, constructor and supervisor in construction industry. The survey to the owners, designers, constructors, and supervisors who are in charge of quality of the 183 architectural projects being constructed has been performed for investigating the importance and actual level of quality and quality factors. Questionnaires are based on the quality factors shown in ISO 9001:2000 international quality management system requirements. There are distinct opinion gaps for quality among owner, designer, constructor, and supervisor who working for the same architectural projects.