An explosive discharge actuated tool includes a piston disposed in a barrel to be driven by a combustion gas for exerting a striking power to strike a fastener out of the barrel. A power adjusting unit is disposed to adjust an opening area of an exhaust port for the combustion gas, and includes an adjusting pin movable longitudinally to completely or partially close the exhaust port so as to adjust the striking power, and an engaging block coupled to the adjusting pin through a latch spindle to be moved transversely to allow or prevent movement of the adjusting pin relative to the exhaust port.