An automatic transmission includes a plurality of planetary gears disposed between an input shaft and an output shaft and having a plurality of rotational elements. A plurality of frictional elements are selectively engaged and released for controlling rotations and connections of the plurality of rotational elements in accordance with instructions so as to realize a plurality of gear positions. A rotational speed detecting section detects a rotational speed of a predetermined one of the plurality of rotational elements other than the input shaft and the output shaft. A frictional element release section releases all of the plurality of frictional elements when it is judged that the rotational speed of the predetermined one of the plurality of rotational elements is higher than a predetermined rotational speed.