An automatic transmission locking mechanism for parking, comprising a detent lever interlocked with and adapted to be turned by a manual shift lever, a rod adapted to be advanced or retracted by the detent lever, a cam slidably mounted on the rod and adapted to push a pawl having a detent to the operating position where the detent engages with a parking gear when the automatic transmission is placed in the parking range, a bracket on which the cam runs and a spring for disengaging the detent from the parking gear and for retaining the pawl at the released position. The spring is disposed in the vicinity of the free end of the pawl and within a plane in which the pole turns, with one end thereof engaged with the free end portion of the pawl and with the other end thereof fixed in a finished hole formed in a stationary part.