To provide a shutter having a viscous braking means having a mechanism which demonstrates no braking effect when the shutter is started to descend, but is capable of limiting the descending speed by the braking effect in the middle of the descending operation.

When a winding shaft 2 is rotated, an adapter 4 is prevented from being rotated by a nut 5 in the middle of the rotation, and the rotation of a second transmission means 7 in a viscous braking means 3 to be engaged with the adapter 4 is prevented. When the second transmission member 7 is stopped, the viscous torque in the direction opposite to that of the rotation of the winding shaft 2 is applied by the effect of an outer plate 9 of a viscous coupling 3, an inner plate 8 and a viscous fluid, and the rotation of the winding shaft 2 is braked.