To provide a position detection cover preventing the incursion of sunlight or wind and rain and preventing the shakiness or the slippage of a rotary shaft in case of driving.

The number of revolutions of a pulley disc slit section 4 is detected by a photo interrupter 5, and when a position control of a screen 19 is made, the position detection cover 6 for protecting a rotary position detection section 2 comprises a position detection cover body 7, a doorstop section 8 and a connector protection cover 20, the position detection cover body 7 has an opening section mounted by avoiding the interference with a pulley rotary shaft bearing member 10 or a rotary pulley 3 in a state to put a pulley rotary shaft 9 on a U-shaped bracket with a member different from the pulley rotary shaft bearing member 10, at the same time, the position detection cover body has a position detection cover fixed section 23 fixed to a unit outside frame section 11 and a photo interrupter fixed section 28 for fixing the photo interrupter 5, and the doorstop section 8 has a doorstop for preventing the uplift or slippage of the pulley rotary shaft 9 with the pulley disc slit section 4.