The present invention is intended to provide a general-purpose display device that is able to display on a display unit easily operating information required for assessing a test operation state, and an application program to be executed by the display device. Accordingly, in this display device which displays on the display unit the operating information of an air conditioner in which an outdoor unit provided with an outdoor heat exchanger and an indoor unit provided with an indoor heat exchanger are connected by a refrigerant pipe and a refrigerant is circulated by a compressor, a control unit of the display device controls the display unit so that time information is displayed horizontally and a first operating information display area and a second operating information display area for displaying first operating information and second operating information, respectively, corresponding to the time information are displayed vertically side by side.