An electronic device comprising: a case; a mobile terminal configured to be coupled with the case and comprising: a controller; a connection port provided at one side of the mobile terminal; a first display; and wherein the case comprises: a first body configured to accommodate at least part of the +mobile terminal; a connector protruding inward at one side of the first body and configured to engage with the connection port when the mobile terminal is accommodated at the first body; a second body comprising a second display; and a wiring unit electrically connecting the first body and the second body and configured to transfer a signal from the mobile terminal to the second display, wherein the controller of the mobile terminal is configured to: detect engagement between the connector and the connection port; transmit a signal to the second display for switching the second display to an active state when a first preset touch is received at the first display or the second display; generate a first sub stack and insert into the first sub stack a task related to screen information to be displayed at the second display; generate a second main stack and insert into the second main stack a task related to a first application in response to execution of the first application; generate a second sub stack and insert into the second sub stack a task related to a second application in response to execution of the second application, while the first sub stack for the screen information at the second display is maintained; cause the first display to display first screen information corresponding to the task inserted into the second main stack; and cause the second display to display second screen information corresponding to the task inserted into the second sub stack. a case; a mobile terminal configured to be coupled with the case and comprising: a controller; a connection port provided at one side of the mobile terminal; a first display; and a controller; a connection port provided at one side of the mobile terminal; a first display; and a first body configured to accommodate at least part of the +mobile terminal; a connector protruding inward at one side of the first body and configured to engage with the connection port when the mobile terminal is accommodated at the first body; a second body comprising a second display; and a wiring unit electrically connecting the first body and the second body and configured to transfer a signal from the mobile terminal to the second display, detect engagement between the connector and the connection port; transmit a signal to the second display for switching the second display to an active state when a first preset touch is received at the first display or the second display; generate a first sub stack and insert into the first sub stack a task related to screen information to be displayed at the second display; generate a second main stack and insert into the second main stack a task related to a first application in response to execution of the first application; generate a second sub stack and insert into the second sub stack a task related to a second application in response to execution of the second application, while the first sub stack for the screen information at the second display is maintained; cause the first display to display first screen information corresponding to the task inserted into the second main stack; and cause the second display to display second screen information corresponding to the task inserted into the second sub stack.