Diagnosis device and diagnosis method

A diagnosis device comprising:

• an acquisition unit configured to acquire, from a plurality of internal combustion engine devices, cumulative data for each parameter related to stress acting on a purification device configured to purify exhaust gas of an internal combustion engine and an exhaust gas temperature of the exhaust gas raised for purification;
• a damage degree identification unit configured to identify a degree of damage to the purification device based on the acquired cumulative data;
• a relationship identification unit configured to identify a relational expression indicating a relationship between the identified degree of damage and the exhaust gas temperature;
• an exhaust gas temperature acquisition unit configured to acquire an exhaust gas temperature of exhaust gas raised for purification performed by the purification device from a target device which is an internal combustion engine device to be diagnosed;
• and
• an estimation unit configured to estimate a degree of damage to the purification device of the target device based on the exhaust gas temperature of the target device acquired by the exhaust gas temperature acquisition unit and the relational expression identified by the relationship identification unit.