In this study, the Maker Competency Instrument (MCI) was developed to diagnose the level of Maker Competence of elementary and secondary students in South Korea. First, in this study, a draft of the test tool was adapted based on the Maker Competency Model developed as part of Yoon et al.'s research (2018). Then, two expert-level Delphi surveys examined the content validity of the MCI. To verify the construct's validity, the exploratory factor analysis and the confirmatory factor analysis were conducted in two separate stages with the involvement of both teachers and professional Makers. As a result, it was confirmed by the MCI that 6 higher-order factors (Making mind, Making practice, collaboration, visual thinking, human-orientation, integrated thinking), 19 lower-order factors (observation, sense of challenge, interest in various areas, pleasure of the making process, understanding programming, understanding electricity, information searching, direct execution, understanding production tools, planning, hand knowledge, conflict management, communication, sharing, visual thinking and insight, humanity, user-oriented, analytical thinking, intuitive thinking), and 57 items were reasonable. From the outcome of this paper, it can be deduced that the MCI can be used from elementary to secondary school due to its proven reliability and validity.