An electronic control apparatus includes a controller, a storage, a calculator, and an estimator. The estimator estimates a potential travelling pattern of a vehicle based on a vehicle state during a start-up period. The start-up period is a preliminarily determined period of time right after a turning on of an ignition switch and the potential travelling pattern is an estimated travelling pattern under which the vehicle travels after an elapse of the start-up period. The estimator estimates the potential travelling pattern of the vehicle based on database-stored reference information that indicates a relationship between the vehicle state during the start-up period and an actual travelling pattern of the vehicle after the elapse of the start-up period. When the estimator estimates that the potential travelling pattern of the vehicle is the short distance travel, the controller forcibly starts the malfunction diagnostic before the predetermined diagnostic start condition is satisfied.