Electronic Control Device

A temperature of a catalyst (EHC) is estimated with high accuracy. An electronic control device of the present invention controls an engine system that includes: an internal combustion engine; a motor capable of motoring the internal combustion engine; a catalyst that is installed in an exhaust passage of the internal combustion engine, has a function of being heated by energization, and purifies exhaust gas; and a downstream temperature sensor installed on the downstream side of the catalyst. The electronic control device includes: a control unit that causes the motor to motor the internal combustion engine; and an estimation unit that performs a first estimation process of estimating a temperature of the catalyst based on detection information of the downstream temperature sensor when the internal combustion engine is motored.