A lighting device comprising: an electric power conversion unit comprising a switching element, configured to adjust load electric power that is supplied to a light source load using DC electric power as an input by ON/OFF of said switching element; a current detection unit configured to detect load current that flows through said light source load; a control unit configured to control an operation of said electric power conversion unit by applying a drive signal to said switching element so that said load current that flows through said light source load becomes a constant value proportional to an electric power setting value that determines a size of electric power that is to be supplied to said light source load; a load electric power calculation unit configured to obtain a load electric power of said light source load using said electric power setting value; characterized by further comprising: a voltage detection unit configured to detect load voltage that is applied to said light source load; wherein the control unit is configured to control an operation of said electric power conversion unit using a current detection value that is detected by said current detection unit; wherein the load electric power calculation unit is configured to obtain load electric power of said light source load further using a voltage detection value that is detected by said voltage detection unit; and by further comprising: an input electric power estimation unit configured to estimate the input electric power based on the obtained load electric power and to correct the input electric power by adding a constant value representative of the circuit loss; and a notification unit configured to notify an external device of a calculation result that is obtained in said input electric power estimation unit by means of a notification signal. an electric power conversion unit comprising a switching element, configured to adjust load electric power that is supplied to a light source load using DC electric power as an input by ON/OFF of said switching element; a current detection unit configured to detect load current that flows through said light source load; a control unit configured to control an operation of said electric power conversion unit by applying a drive signal to said switching element so that said load current that flows through said light source load becomes a constant value proportional to an electric power setting value that determines a size of electric power that is to be supplied to said light source load; a load electric power calculation unit configured to obtain a load electric power of said light source load using said electric power setting value; characterized by further comprising: a voltage detection unit configured to detect load voltage that is applied to said light source load; wherein the control unit is configured to control an operation of said electric power conversion unit using a current detection value that is detected by said current detection unit; wherein the load electric power calculation unit is configured to obtain load electric power of said light source load further using a voltage detection value that is detected by said voltage detection unit; and by further comprising: a voltage detection unit configured to detect load voltage that is applied to said light source load; wherein the control unit is configured to control an operation of said electric power conversion unit using a current detection value that is detected by said current detection unit; wherein the load electric power calculation unit is configured to obtain load electric power of said light source load further using a voltage detection value that is detected by said voltage detection unit; and by further comprising: an input electric power estimation unit configured to estimate the input electric power based on the obtained load electric power and to correct the input electric power by adding a constant value representative of the circuit loss; and a notification unit configured to notify an external device of a calculation result that is obtained in said input electric power estimation unit by means of a notification signal.