PURPOSE: To make execution of installation work easy by a method wherein a canvas support arm is provided, through a pair of expandable/contractile arms, to a support arm fixed to a wall surface, and a canvas wound round a wind-up drum is attached to the canvas support arm.

CONSTITUTION: Elastic holding mechanisms 9 for extending expandable/ contractile arms 4 within the limit of stretching of a canvas 8 and a worm reduction gearing 13 connected to a wind-up drum 7 for transmitting rotation of a driving shaft 14 are provided. The worm reduction gearing 13 is constructed of a worm wheel 13A connected to a rotation operating shaft 10 and a worm 13B formed approximately integral with the driving shaft 14 for meshing with the worm wheel 13A. When unwinding the canvas 8 from the wind-up drum 7, the rotation operating shaft 10 is rotated through the worm reduction gearing 13 with the driving shaft 14 rotated, and the wind-up drum 7 is rotated by operation of energizing force of the elastic holding mechanisms 9. Therefore, installation can be executed without the need for adjustment such as rewinding in a specified number of windings.