A transmission operating apparatus for automatic transmission wherein, when a shift lever of the automatic transmission is shifted to a specific position such as a parking position, a detent pin provided for the shift lever is engaged with a movable body and is moved to a first position so as to be engaged with detent means so that the shift to another shift position is prevented. A lock is engaged with the movable body which has been moved, together with the detent pin, to the first shift position so that the lock means cannot be separated from the movable body if a driver does not perform any special operation such as footing the brake or the like. Therefore, the movable body cannot be moved to the second position, and the shift lever cannot be moved to another shift position. The movable body is positioned at the second position when the shift lever is positioned at another shift position, while the same is engaged with the detent pin immediately after the shift lever is operated to the specific position.