A diagnostic system for diagnosing energy saving that has an evaluation mode and is configured to monitor a use amount of an energy resource selected from a group consisting of electricity and gas used by a load, the diagnostic system comprising: a control unit configured to output a control command to adjust the use amount in accordance with predetermined schedule control information; an information acquisition unit configured to, periodically, obtain information for obtaining the use amount used by said load as use information; an information storage unit configured to store time series data in which the use information is associated with at least a date on which the use information is obtained; a schedule setting unit configured to set the schedule control information; and a display unit, characterized by a comparison and evaluation unit configured: to compare the use amounts on either side of a reference point when the evaluation mode is set; to set a point in time at which the schedule control information is modified by said schedule setting unit as the reference point; to read out the use information obtained over a predetermined period before the reference point from the data holding area of the information storage unit where the use information is stored in time series and to set the read use information as reference data, wherein the reference data are generated so as to exclude use information obtained on a special day on which the use amount differs from normal, the special day being a store holiday or a day on which opening hours differ from normal opening hours, wherein if the predetermined period before the reference point includes the special day, the use information is obtained over another predetermined period a unit of time before the predetermined period; to read out the use information obtained over the aforementioned predetermined period after the reference point from the data holding area of the information storage unit where the use information is stored in time series and to set the read use information as performance data; and to cause said display unit to display an energy saving effect brought about by modifying the schedule control information on the basis of the performance data and the reference data. a control unit configured to output a control command to adjust the use amount in accordance with predetermined schedule control information; an information acquisition unit configured to, periodically, obtain information for obtaining the use amount used by said load as use information; an information storage unit configured to store time series data in which the use information is associated with at least a date on which the use information is obtained; a schedule setting unit configured to set the schedule control information; and a display unit, characterized by a comparison and evaluation unit configured: to compare the use amounts on either side of a reference point when the evaluation mode is set; to set a point in time at which the schedule control information is modified by said schedule setting unit as the reference point; to read out the use information obtained over a predetermined period before the reference point from the data holding area of the information storage unit where the use information is stored in time series and to set the read use information as reference data, wherein the reference data are generated so as to exclude use information obtained on a special day on which the use amount differs from normal, the special day being a store holiday or a day on which opening hours differ from normal opening hours, wherein if the predetermined period before the reference point includes the special day, the use information is obtained over another predetermined period a unit of time before the predetermined period; to read out the use information obtained over the aforementioned predetermined period after the reference point from the data holding area of the information storage unit where the use information is stored in time series and to set the read use information as performance data; and to cause said display unit to display an energy saving effect brought about by modifying the schedule control information on the basis of the performance data and the reference data. to compare the use amounts on either side of a reference point when the evaluation mode is set; to set a point in time at which the schedule control information is modified by said schedule setting unit as the reference point; to read out the use information obtained over a predetermined period before the reference point from the data holding area of the information storage unit where the use information is stored in time series and to set the read use information as reference data, wherein the reference data are generated so as to exclude use information obtained on a special day on which the use amount differs from normal, the special day being a store holiday or a day on which opening hours differ from normal opening hours, wherein if the predetermined period before the reference point includes the special day, the use information is obtained over another predetermined period a unit of time before the predetermined period; to read out the use information obtained over the aforementioned predetermined period after the reference point from the data holding area of the information storage unit where the use information is stored in time series and to set the read use information as performance data; and to cause said display unit to display an energy saving effect brought about by modifying the schedule control information on the basis of the performance data and the reference data.