In our body, the tumor tissue is surrounded by blood vessels, extracellular matrix and various cells. However, in many cases, the experiment about cancer is carried out by culturing the cancer cells in a flat or simple three-dimensionally without regard to the in vivo environment. In this study, using microwells of various sizes to confine the tumoroid spatially, the biological and physical factors that are results of controlling the compactness are observed. Furthermore, I confirmed that the drug resistance increases as the degree of compactness increases and I propose a method to reduce the drug resistance. Thus, my thesis contributes to the study of overcoming drug resistance, one of the obstacles of cancer treatment, and finding effective cancer therapy.