To provide a shutter obstruct detector of a simple constitution, inexpensive manufacturing costs, and easy maintenance.

A seat plate main body 2 is provided for a lower end part of a shutter main body 1, and a movable back plate 3 freely movable in vertical directions is provided below the seat plate main body 2. A wire 7 is extended between an opening/closing machine 5 of a take-up shaft 4 of the shutter main body 1 and a wire reel 6 provided for a lower end part of the shutter main body 1. A holding mechanism 8 is constituted of both a fixed part 9 fixed to the shutter main body 1 and a rod part 10 which is supported at the movable back plate 3 and of which an upper end part is protruded immediately below the fixing part 9. The wire 7 is passed between the fixed part 9 and the rod part 10. When the movable back plate 3 comes into contact with an obstruction when lowered, the wire 7 is strongly held between the rod part 10 and the fixed part 9 to halt the opening/closing machine 5 with a tensile force acting on the wire 7 by the own weight of the shutter main body and stronger than it is in normal times and halt the shutter main body 1.