To control display or hiding of windows simultaneously available based on a configuration used by a user. An information-processing device according to the present invention identifies applications that the device is able to execute; and when an instruction to display a window (a subject window) is performed, the device obtains a relevance information list of applications to display the subject window (subject applications). In the relevance information list, information for determining an application relating to the subject application is described. The information-processing device determines whether an application described in the relevance information list is included in the executable applications, and if it is included in the executable applications, the device displays a window of the application (a simultaneous display window) together with the subject window. Also, when the information-processing device receives an instruction to hide the subject window, the device hides the subject window and the simultaneous display window.