A controller is configured to accept a user input from an input interface, access a memory storing tree information that includes pieces of information about a plurality of hierarchized elements, and generate a screen command related to a display screen of a display. The controller causes elements included in the tree information to be displayed on the display. When an element located in the center in the width direction of the display receives an expanding operation, child elements are expanded one layer below the element. When a parent element of child elements goes beyond the center in the width direction, in response to the width direction slide operation, the child elements subordinate to the element are hidden on the display.