CATALYST TEMPERATURE CALCULATING DEVICE, AND CONTROLLER FOR INTERNAL COMBUSTION ENGINE

A catalyst having an oxygen storage capacity is provided in an exhaust passage of an internal combustion engine. A catalyst temperature calculating device calculates an oxygen storage amount of the catalyst to a value greater than or equal to zero and less than or equal to than a maximum value based on an amount of oxygen and an amount of unburned fuel components in a fluid flowing into the catalyst. A temperature calculation process calculates a temperature of the catalyst assuming that an amount of temperature rise of the catalyst is larger when an increase amount of the oxygen storage amount is large than when the increase amount of the oxygen storage amount is small in a case where the oxygen storage amount increases.