PURPOSE: To prevent the damage of a tape-like switch and to enable the opening of a shutter curtain in the case of service interruption by interlocking with the change-over to a lock releasing position of a latch bar to make unable obstacle detecting operation through an obstacle detection member.

CONSTITUTION: A shutter curtain is energized to an open side by energizing force of a balance spring within range of totally enclosed vicinity, so when a latch bar 17 is switched to a lock releasing position B to hold under the blockage, the shutter curtain is slightly opened without providing any external force. Under such a condition, the shutter curtain is manually opened by lifting an obstacle detection member 11 under the curtain by hand. At that time, the lower end of a restraining member 25 is made to approach and face to the upper end of the detection member 11 with the change-over to the lock releasing position B of the latch bar 17, and detecting operation of the detection member 11 becomes unable. Accordingly, a pushing member 15 of a switch pushing means 12 is projected, and a switch 4 is not pushed.