CONTROLLER AND CONTROL METHOD FOR VEHICLE

A controller is configured to control a vehicle that includes an internal combustion engine and an automatic transmission. The controller is configured to execute a shifting process that switches a gear ratio of the automatic transmission and a lean operation process that operates the internal combustion engine with an air-fuel ratio of the air-fuel mixture in a cylinder leaner than a stoichiometric air-fuel ratio. The controller is further configured to, when executing the shifting process during execution of the lean operation process, set an air-fuel ratio in a case in which the shifting process is being executed to a value closer to the stoichiometric air-fuel ratio than an air-fuel ratio in a case in which the shifting process is not being executed.