The KEK Research Building No. 4 is a specialized experimental and research facility completed in 2000 at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Ibaraki Prefecture. Designed collaboratively by Ueno and Fujii Architects and the KEK Facilities Department under the Ministry of Education, this structure exemplifies functional modernist architecture tailored to advanced scientific research. The building supports the institution's cutting-edge particle physics work, featuring specialized laboratory spaces and infrastructure designed to accommodate sophisticated experimental equipment. Its design reflects the technical and organizational demands of contemporary high-energy physics research, making it a notable example of late 20th-century institutional architecture in Japan.