This study examined the qualities of an effective teacher needed to accomplish educational reform successfully and prepare for a rapidly changing knowledge-based society. To achieve the purpose of the study, the following specific questions were looked into; (1) knowledge, skills, attitude of an effective teacher. (2) a proposal for staff development programs to improve the effectiveness of teachers. (3) a proposal to support teachers' efforts to improve their effectiveness. (4) the factors inhibiting the improvement of teachers' effectiveness. In this study, 'in-depth interview' was used for data collection because the study deals with the "subjective consciousness" of teachers, and qualitative research methods are useful to such a case. The research was done on teachers from secondary schools in Pusan City. According to the teachers interviewed, an effective teacher needed in the new age has such knowledge, skills, and attitude as; (1) knowledge in their major, general culture and common sense, psychology of educational counselling, social science, and knowledge and information related to curriculum. (2) effective instruction skills, skills to guide student behavior, skills related to administrative clerical work, using the computers, extra curriculum activities, educational evaluation, using teaching materials, developing educational programs, and good communication skills. (3) attitude relevant to willingness to understand and converse with students at their cognitive level, positive expectations and concern toward students, democratic problem solving, continuous self-study and development, thoroughgoing mission and professionalism, will for educational reform and innovation, neat appearance and refined language, and successful interpersonal relationships. The teachers also said that the current staff development system, as a program to provide necessary qualities for teachers, has improved in the last 3 years through diverse curriculum and systematic programs. However, due to the problematic promotion system, the staff development program has turned into just a 'point collecting' game from the role of in-service training program; teachers take training courses as the means just collecting points for promotion purpose. Factors inhibiting the improvement of teachers are (1) overload of formal paperwork over emphasizing outcome, (2) mannerism of teachers not perceiving their lack of professionalism, (3) the general attitude in the teaching profession resisting change and reform, (4) supervisory activities lacking rigid regulation, (5) research just as the means of point-collection only for promotion, and (6) staff development programs lacking efficiency. These factors, interacting each other, inhibited the improvement of teachers.