PURPOSE: To provide an air bag pressure adjusting device by which the buffering performance of the air bag after the expansion of the bag is heightened.

CONSTITUTION: The air bag pressure adjusting device consists of a collision detecting means A1, which detects the collision of a vehicle, an expanding means A3, which expands an air bag A2 following the collision detecting action of the collision detecting means A1, a judging means A4, which judges that the expansion of the air bag A2 has been completed after the expanding action of the collision detecting means A3, an exhaust port A5, which is provided behind the air bag A2, a lid A6, which is locked at the position to close the exhaust port A5, and a lid opening means A7, which releases the locking of the lid A6 as soon as the judging means A4 judges that the expansion of the air bag A2 has been completed.