A HMI development support device, comprising: a HMI editing unit, configured to perform editing of a HMI project that is configured by a plurality of objects; a display unit, configured to display an editing screen of the HMI project; and a temporary storage unit, configured to temporarily store the HMI project being edited, wherein the HMI editing unit comprises a comparison processing unit, configured to form a comparison screen for highlighting differences between a reference HMI project and the HMI project being edited, and for displaying the comparison screen on the display unit, wherein the comparison screen is a screen that is configured to highlight different attribute values in objects of the reference HMI project and objects of the HMI project being edited; the HMI development support device being characterized in that the comparison processing unit comprises a merge processing unit, configured to replace, if the attribute values of the HMI project being edited are selected, only the attribute values of the objects of the HMI project being edited that are differences with the attribute values of the objects having same variables in the reference HMI project, wherein the attribute values of the objects comprise properties, event actions, or animations of the objects, wherein the merge processing unit is configured to replace, if an object of the HMI project being edited is selected, attribute values which are differences in the selected object with attribute values of the objects having same variables in the reference HMI project, wherein on receiving cancel of processing for replacing the attribute values, the merge processing unit is configured to return to the HMI project being edited that is read out from the temporary storage unit, wherein the display unit is configured to display, in the comparison screen, an arrangement of the objects of the reference HMI project and the attribute values of the objects of the reference HMI project in parallel, an arrangement of the objects of the HMI project being edited and the attribute values of the objects of the HMI project being edited in parallel, and the attribute values of the objects of the reference HMI project and the attribute values of the objects of the HMI project being edited in adjacent, wherein the display unit is configured to display, in the comparison screen, the arrangement of the objects of the reference HMI project and the arrangement of the objects of the HMI project being edited to clamp the attribute values of the objects of the reference HMI project and the attribute values of the objects of the HMI project being edited, the attribute values of the objects of the reference HMI project and the attribute values of the objects of the HMI project being edited are displayed in form of a list. a HMI editing unit, configured to perform editing of a HMI project that is configured by a plurality of objects; a display unit, configured to display an editing screen of the HMI project; and a temporary storage unit, configured to temporarily store the HMI project being edited, wherein the HMI editing unit comprises a comparison processing unit, configured to form a comparison screen for highlighting differences between a reference HMI project and the HMI project being edited, and for displaying the comparison screen on the display unit, a merge processing unit, configured to replace, if the attribute values of the HMI project being edited are selected, only the attribute values of the objects of the HMI project being edited that are differences with the attribute values of the objects having same variables in the reference HMI project, wherein the attribute values of the objects comprise properties, event actions, or animations of the objects, wherein the merge processing unit is configured to replace, if an object of the HMI project being edited is selected, attribute values which are differences in the selected object with attribute values of the objects having same variables in the reference HMI project, wherein on receiving cancel of processing for replacing the attribute values, the merge processing unit is configured to return to the HMI project being edited that is read out from the temporary storage unit, wherein the display unit is configured to display, in the comparison screen, an arrangement of the objects of the reference HMI project and the attribute values of the objects of the reference HMI project in parallel, an arrangement of the objects of the HMI project being edited and the attribute values of the objects of the HMI project being edited in parallel, and the attribute values of the objects of the reference HMI project and the attribute values of the objects of the HMI project being edited in adjacent, wherein the display unit is configured to display, in the comparison screen, the arrangement of the objects of the reference HMI project and the arrangement of the objects of the HMI project being edited to clamp the attribute values of the objects of the reference HMI project and the attribute values of the objects of the HMI project being edited, the attribute values of the objects of the reference HMI project and the attribute values of the objects of the HMI project being edited are displayed in form of a list.