<p> 1. The purpose of this paper: is to reconstruct the design process of Yonago Public Hall (1958) and to reveal architects’ formal manipulations which must imply their strategic design thinking.</p><p> 2. The study material: was the total 230 of original design sketches and drawings possessed by Kyoto Institute of Technology.</p><p> 3. The methodology: was focused on the morphological tool used to solve the design tasks. The idea of transformability (potential transformation possibility which the designer thought at design) was proposed and explained which may appear as simultaneous formal variation or sequential formal changes.</p><p> 4. The chronological order of the design sketches and drawings: was established by date inscriptions and formal matchings as Table 1 and 2. The partial processes called "study" were subdivided according to sketching and depicted shape identities.</p><p> 5. The morphological analysis on transformability: was discussed as follows:</p><p> [Study 1] on building distribution on the site: shows dynamic variation as see in Fig. 4. Civic quarter was used as a connector bridging main and smaller halls and various shapes for exterior space were tested.</p><p> [Study 2] on sectional composition and the structure of the main hall: shows the transformations related to sight and projection lines and induced various structural modulations appeared in Fig. 5.</p><p> [Study 3] on integration attempt of the main hall and civic quarter: shows the elimination of the smaller hall and thus floorage reduced. The building form became integrated into a simple rectangle as see in Fig. 7.</p><p> [Study 4] on disintegration attempt of the civic quarter from the main hall: shows disintegration process of the civic quarter from the main hall. The civic quarter go laterally along the hall first, then it was displaced to the backside as see in Fig. 8. As the result, the interior volume of the hall was exposed and became the principal manifestation of the design. The structure of the main hall opened like fan shape, and final composition realized.</p><p> [Study 5] concluding schematic design: shows geometric adaptation and detailing attempt to finalize the schematic design as see in Fig. 9. A model was prepared for the presentation held at the Yonago-city on Dec. 1956 as see in Fig. 10. Perspective drawing of Fig. 11 was published in new year issue of Yonago-city news letter.</p><p> [Study 6] concluding working design: shows very limited changes as see in Fig. 12, which are: shell structure application to roof and side walls, direction change of outside evacuation staircase, and elaboration of the foyer column section. The working drawings were prepared in the end of Feb. 1957, although additional drawings were going to be issued even after the construction started in Apr. 1957.</p><p> Total formal manipulation conducted by the architects: was charted as Table 3 and relevant notices were pointed as follows:</p><p> 1）In the first 2 studies, the architect scanned wide range of transformability, yet it became more and more specific in late studies.</p><p> 2）The dramatic formal change in the [Study 4] was predicted in preliminary sketches in the early [Study 1 and 2].</p><p> 3）Design thinking in adopting to the requirements was observed such as: effective use of exterior space, continuity / separation of the main hall and civic quarter, ensuring appropriate sightline / evacuation route and constant reduction of floorage.</p>