A tree-information-providing device comprising a control unit configured to accept a user input from an input interface, access a memory (22, 24, 26) that stores tree information that includes pieces of information about many hierarchized elements, and generate a screen command related to a display screen of a display, wherein the control unit is configured to execute: a process for causing the elements included in the tree information to be displayed on the display, in response to a user input for display of the elements; a process for accepting a user input for an expanding operation for any of the elements displayed on the display; characterised by a process for, in response to the expanding operation, displaying the element targeted by the expanding operation in a vertical reference region extending in a longitudinal direction, the vertical reference region being defined at a particular position in a width direction of the display; a process for expanding child elements in a width direction region extending in the width direction one layer below the element on the display, if the element displayed in the vertical reference region has received the expanding operation, and one or more child elements are subordinate to the element on a layer lower than the element in the tree information; a process for accepting a user input for a width direction slide operation; a process for causing all the elements included in the width direction region, which are targeted by the width direction slide operation, to laterally slide together in the width direction, in response to the width direction slide operation; and a process for causing child elements subordinate to an element that has gone beyond the vertical reference region in the width direction to be hidden on the display. a process for causing the elements included in the tree information to be displayed on the display, in response to a user input for display of the elements; a process for accepting a user input for an expanding operation for any of the elements displayed on the display; characterised by a process for, in response to the expanding operation, displaying the element targeted by the expanding operation in a vertical reference region extending in a longitudinal direction, the vertical reference region being defined at a particular position in a width direction of the display; a process for expanding child elements in a width direction region extending in the width direction one layer below the element on the display, if the element displayed in the vertical reference region has received the expanding operation, and one or more child elements are subordinate to the element on a layer lower than the element in the tree information; a process for accepting a user input for a width direction slide operation; a process for causing all the elements included in the width direction region, which are targeted by the width direction slide operation, to laterally slide together in the width direction, in response to the width direction slide operation; and a process for causing child elements subordinate to an element that has gone beyond the vertical reference region in the width direction to be hidden on the display.