A window blind includes an input mechanism adapted to change a location of a bottom rail, an adjustment output mechanism adapted to be motivated when the bottom rail is located at a low position, whereby to tilt slats between two positions, and an output clutch mechanism, which is adapted to be driven by the input mechanism to move the bottom rail toward a high position, and is adapted to be driven by the input mechanism to move the bottom rail toward the low position when it is at the high position. A stroke delay mechanism is provided on a transmission path from the adjustment output mechanism to the output clutch mechanism, which is adapted to delay an affected time for transmission. Whereby, only one single control module is required to adjust the inclination angle of the slats and to collect and expand the covering material.