A maintenance monitor device configured to display a graph of numerical data of three or more of a plurality of display items related to a diesel engine mounted on an industrial vehicle simultaneously on a monitor screen, the three or more of a plurality of display items being selected optionally from display items related to the diesel engine, the maintenance monitor device comprising: a list display unit configured to display a list of the display items on the monitor screen; a display item selection unit configured to optionally select three or more display items from the list of the display items, a numerical data display unit configured to be capable of displaying a graph of numerical data related to the three or more display items on the monitor screen in accordance with graph axes, the graph axes including a first axis which includes a time axis and a second axis which includes a scale being different depending on the display item; a position information calculation unit configured to calculate position information of a cursor displayed on the monitor screen; a display item recognition unit configured to recognize one of the display items indicated by the cursor on the monitor screen, on the basis of the position information of the cursor calculated by the position information calculation unit; and a second axis display unit configured to display only one scale corresponding to the recognized one of the display items recognized by the display item recognition unit on the second axis included in the graph axes, wherein the display item recognition unit is configured to recognize, when the cursor overlaps with one of the display items displayed on the list of the display items, the one of the display items overlapping with the cursor as the one of the display items indicated by the cursor if the one of the display items overlapping with the cursor is one of the display items selected by the display item selection unit, and wherein the display item recognition unit is configured not to recognize, when the cursor overlaps with one of the display items displayed on the list of the display items, the one of the display items overlapping with the cursor as the one of the display items indicated by the cursor if the one of the display items overlapping with the cursor is not one of the display items selected by the display item selection unit. a list display unit configured to display a list of the display items on the monitor screen; a display item selection unit configured to optionally select three or more display items from the list of the display items, a numerical data display unit configured to be capable of displaying a graph of numerical data related to the three or more display items on the monitor screen in accordance with graph axes, the graph axes including a first axis which includes a time axis and a second axis which includes a scale being different depending on the display item; a position information calculation unit configured to calculate position information of a cursor displayed on the monitor screen; a display item recognition unit configured to recognize one of the display items indicated by the cursor on the monitor screen, on the basis of the position information of the cursor calculated by the position information calculation unit; and a second axis display unit configured to display only one scale corresponding to the recognized one of the display items recognized by the display item recognition unit on the second axis included in the graph axes, wherein the display item recognition unit is configured to recognize, when the cursor overlaps with one of the display items displayed on the list of the display items, the one of the display items overlapping with the cursor as the one of the display items indicated by the cursor if the one of the display items overlapping with the cursor is one of the display items selected by the display item selection unit, and wherein the display item recognition unit is configured not to recognize, when the cursor overlaps with one of the display items displayed on the list of the display items, the one of the display items overlapping with the cursor as the one of the display items indicated by the cursor if the one of the display items overlapping with the cursor is not one of the display items selected by the display item selection unit.