A controller for an engine controls a throttle opening degree. The controller includes a target opening degree calculating section that selects either a primary request value for a throttle opening degree that corresponds to a torque request or a secondary request value that corresponds to another request and that calculates a target throttle opening degree from the selected one of the first and secondary request values. If the primary request value has been selected, an abnormality occurrence determining section determines whether or not an abnormality has occurred, in accordance with a magnitude of a deviation of the primary request value from the target throttle opening degree. If the secondary request value has been selected, the abnormality occurrence determining section determines whether or not an abnormality has occurred, in accordance with whether or not the target throttle opening degree is greater than or equal to a predetermined upper limit value.