Providing an energy-saving diagnostic system with which an energy saving effect brought about by modifying schedule control information can be confirmed easily. A comparison and evaluation unit 28 sets a point in time at which schedule control information is modified by a schedule setting unit 25, as a start point of an evaluation mode. When the evaluation mode starts, the comparison and evaluation unit 28 sets use information obtained over a predetermined period (i.e. in units of days, weeks, months, or years) before the start point of the evaluation mode as reference data, sets use information obtained over the predetermined period after the start point as performance data, and compares the reference data with performance data constituted. The comparison and evaluation unit 28 outputs a comparison data and to cause a user terminal 3 to display the energy saving effect brought about by modifying the schedule control information.