A processing device configured to decide a winding temperature calculation model, the calculation model being included in an electronic thermal unit for a motor that has a stator around which a winding is wound and a rotor to estimate a temperature of the winding and characterized in that the calculation model includes a winding temperature characteristic model that includes winding-related parameters in relation to temperature characteristics of the winding and a stator temperature characteristic model that includes stator-related parameters in relation to temperature characteristics of the stator and in that the processing device comprises: a temperature transition acquisition unit configured to acquire a rising temperature transition of the temperature of the winding in a state in which a first voltage is applied in order to raise the temperature of the winding to a first temperature and further acquires a falling temperature transition of the temperature of the winding in a state in which a second voltage is applied in order to lower the temperature of the winding to a second temperature that is lower than the first temperature after the temperature of the winding converges on the first temperature; and a decision unit configured to calculate the stator-related parameters on the basis of the falling temperature transition to decide the stator temperature characteristic model and further to calculate the winding-related parameters on the basis of the rising temperature transition and the decided stator temperature characteristic model to decide the winding temperature characteristic model. the calculation model includes a winding temperature characteristic model that includes winding-related parameters in relation to temperature characteristics of the winding and a stator temperature characteristic model that includes stator-related parameters in relation to temperature characteristics of the stator and in that the processing device comprises: a temperature transition acquisition unit configured to acquire a rising temperature transition of the temperature of the winding in a state in which a first voltage is applied in order to raise the temperature of the winding to a first temperature and further acquires a falling temperature transition of the temperature of the winding in a state in which a second voltage is applied in order to lower the temperature of the winding to a second temperature that is lower than the first temperature after the temperature of the winding converges on the first temperature; and a decision unit configured to calculate the stator-related parameters on the basis of the falling temperature transition to decide the stator temperature characteristic model and further to calculate the winding-related parameters on the basis of the rising temperature transition and the decided stator temperature characteristic model to decide the winding temperature characteristic model. a temperature transition acquisition unit configured to acquire a rising temperature transition of the temperature of the winding in a state in which a first voltage is applied in order to raise the temperature of the winding to a first temperature and further acquires a falling temperature transition of the temperature of the winding in a state in which a second voltage is applied in order to lower the temperature of the winding to a second temperature that is lower than the first temperature after the temperature of the winding converges on the first temperature; and a decision unit configured to calculate the stator-related parameters on the basis of the falling temperature transition to decide the stator temperature characteristic model and further to calculate the winding-related parameters on the basis of the rising temperature transition and the decided stator temperature characteristic model to decide the winding temperature characteristic model.