In a medical image managing system, there are first and second density conversion modes. In the first density conversion mode, a medical image is processed in density conversion by an image server, before a density-converted medical image is transmitted to a client terminal. In the second density conversion mode, a medical image is transmitted from the image server to the client terminal, which processes the medical image in the density conversion. A density conversion mode checker compares processing time of the first density conversion mode with processing time of the second density conversion mode after acquisition according to communication speed between the image server and the client terminal, and processing speeds of the client terminal and the image server. One of the density conversion modes with the shorter processing time is selected. Thus, the density-converted medical image can be displayed rapidly at the client terminal.