A diagnosis apparatus for diagnosing deterioration of a DC link capacitor of an inverter having the DC link capacitor and an inverter part, the diagnosis apparatus comprising: a current detector configured to detect a current supplied to a motor in the inverter part; a switching mode power supply, SMPS, configured to supply a DC voltage and to be coaled to the DC link capacitor; and a controller configured to control the DC voltage supplied from the SMPS to the motor to have a predetermined initial level, the controller being arranged to estimate the of a ratio of a deteriorated capacitance to an initial capacitance of the DC link capacitor, by considering power consumption due to a resistance of the motor, causing a power consumption of a load, power consumption of the SMPS and a switching loss of the inverter part, wherein the estimation includes, in response to the voltage of the DC link capacitor reaching a predetermined final level: determining a first factor, k old, based on a ratio of power consumption of the SMPS and switching loss to power consumption of the load using the deteriorated capacitance of the DC link capacitor, determining a second factor, k ini, based on a ratio of power consumption of the SMPS and switching loss to power consumption of the load using the initial capacitance of the capacitor, determining a first product by multiplying the first factor, k old, with the rate of power consumption of the load using the deteriorated capacitance of the DC link capacitor, determining a second product by multiplying the second factor, k ini, with the rate of power consumption of the load using the initial capacitance of the DC link capacitor, determining a quotient of the first and second products so as to diagnose the DC link capacitor. a current detector configured to detect a current supplied to a motor in the inverter part; a switching mode power supply, SMPS, configured to supply a DC voltage and to be coaled to the DC link capacitor; and a controller configured to control the DC voltage supplied from the SMPS to the motor to have a predetermined initial level, the controller being arranged to estimate the of a ratio of a deteriorated capacitance to an initial capacitance of the DC link capacitor, by considering power consumption due to a resistance of the motor, causing a power consumption of a load, power consumption of the SMPS and a switching loss of the inverter part, wherein the estimation includes, in response to the voltage of the DC link capacitor reaching a predetermined final level: determining a first factor, k old, based on a ratio of power consumption of the SMPS and switching loss to power consumption of the load using the deteriorated capacitance of the DC link capacitor, determining a second factor, k ini, based on a ratio of power consumption of the SMPS and switching loss to power consumption of the load using the initial capacitance of the capacitor, determining a first product by multiplying the first factor, k old, with the rate of power consumption of the load using the deteriorated capacitance of the DC link capacitor, determining a second product by multiplying the second factor, k ini, with the rate of power consumption of the load using the initial capacitance of the DC link capacitor, determining a quotient of the first and second products so as to diagnose the DC link capacitor. determining a first factor, k old, based on a ratio of power consumption of the SMPS and switching loss to power consumption of the load using the deteriorated capacitance of the DC link capacitor, determining a second factor, k ini, based on a ratio of power consumption of the SMPS and switching loss to power consumption of the load using the initial capacitance of the capacitor, determining a first product by multiplying the first factor, k old, with the rate of power consumption of the load using the deteriorated capacitance of the DC link capacitor, determining a second product by multiplying the second factor, k ini, with the rate of power consumption of the load using the initial capacitance of the DC link capacitor, determining a quotient of the first and second products so as to diagnose the DC link capacitor.