To miniaturize an actuator when a locking device for locking a shutter curtain on a building frame is designed so that the actuator operated by excitation of a solenoid automatically actuates, for unlocking motion, an unlocking unit for changing the position of locks to an unlocking position disengaged from keepers.

The unlocking unit 15, which is disposed at a lower end of a guide rail 5, comprises an unlocking element 22 for displacing a vertically operable bar 13 for the locks 8 in an opening direction of a shutter curtain 1, a constant load spiral spring 18b for urging the unlocking element 22 in the opening direction, a stopper pin 20d movable in an indoor and an outdoor direction and changeable in the attitude from a restrictive position of restricting a movement of the unlocking element 22 in the opening direction to a permissive position of permitting such a movement as the shutter curtain 1 is in a fully closed position, and the actuator 17 displaceable in an opening and a closing direction upon excitation of the solenoid 17g to change the position of the stopper pin 20d in the restrictive position to the permissive attitude.