Modular construction, which involves factory-based modular unit manufacturing followed by installation at a construction site, has been recognized as one of the sustainable construction methods. Its advantages are known to be implemented through (1) standardized design, (2) standardized production method, and (3) large-scale development (mass production system). These three conditions are basic requirements for modular construction market expansion, but it is difficult to define that these conditions are a prerequisite for judging whether modular construction applied or not. Nevertheless, public development companies in regions or countries where modular construction has just begun thought that modular construction should meet all three conditions that are suitable for applying public construction projects. This is because it is difficult to compare conventional construction projects with similar conditions to modular construction projects. This paper analyzes the cost and duration data of three small-scale public construction rental housing (PCRH) projects involving modular construction in Korea. These cases presented herein include a public college student dormitory, public low-rise rental housing, and public mid-rise rental housing in small-scale development projects. Those were applied not standardized design (common design and regulation), but were reflected in each project’s demands (different design and regulation). To compare it, this paper analyzed 91 public housing provision projects’ construction data from 2011 to 2017 from one of the public rental housing provision companies in Korea. Among them, 19 small-scale public rental housing data were extracted for comparing with modular construction project data. The results show that, even if not standardized, the design and production process, and modular construction durations, were more effective—but costs were similar or expensive. Based on the conclusion drawn from three cases, this paper presents important considerations for the application of modular construction in other small-scale public construction rental housing projects from the perspective of public development companies.