PURPOSE: To permit to reset without exchanging a member even if the blocking mechanism is operated except upon emergency by a method wherein the support of a blocking board is released by the change of configuration of a shape memory alloy when a temperature is higher than a predetermined temperature.

CONSTITUTION: A damper mechanism 30 consists of a support mechanism 33, supporting a damper 32, a release mechanism 34, releasing the support of the damper, and a control circuit 35. The release mechanism 34 is equipped with the shape memory alloy 42 of coil shape, which is arranged at the inside of the duct 31, and provided with an outer tube-like electric heater 43 as well as a flange member 44 guiding the shape memory alloy 42. The control circuit 35, which has detected a signal from a smoke detector or a heat detector, heats the outer tubular electric heater 43 by the conducting operation thereof, the shape memory alloy 42 is heated to elongate it by the shape memory effect thereof when the temperature has become higher than the predetermined temperature, the tip end of a shaft 41 is moved toward the direction of the duct 31 and engagement between a fixed arm 40 and the tip end 47 is released.