In control apparatus and method for an automatic transmission, a gear shift state of a stepwise variable transmission mechanism is controlled to a target gear shift state by releasing a first engagement section according to a reduction in a capacity of the first engagement section and, simultaneously, by engaging a second engagement section according to an increase in the capacity of the second engagement section, in accordance with a torque inputted to the stepwise variable transmission mechanism and, during an inertia phase, either one of the first and second engagement sections functions as a gear shift state control side engagement section and the capacity of a gear shift state non-control side engagement section which is the other engagement section is increased when determining that it is impossible to make the gear shift state follow up the target gear shift state at the gear shift state control side engagement section.