This study started from the question "how does learning occur in human life". In particular, I am interested in learning that takes place continuously anywhere at any time rather than learning that is occurred by being taught by others. This study interpreted critical reflection as learning that continuously occur in anywhere at any time i.e. as informal learning, and then analyzed the process how it takes place in human life. To find out how critical reflection occurs, this study focused on factory workers' critical reflection while working on the shop floor. Using ethnography methodology I analyzed the observed and interviewed data of factory workers' working life in order to examine critical reflection as informal learning. In this process, I used Cultural Historical Activity Theory (CHAT) as the theoretical framework in order to elaborate the process that critical reflection occurs while working. The analysis using CHAT was helpful to find out workers' critical reflection as expansive learning that continuously promotes the other learning. That is, factory workers' learning activity on working life was gradually expanded to the new pattern of activities such as forming good relationship with family or creating identity as a social member. Using the expansive learning based on CHAT, I examined critical reflection as continuously being occurred anywhere at any time, and suggested it as informal learning that can take place in the workplace. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]