A window blind includes a stationary seat, a blind mechanism, a coupling mechanism and a control pole. The blind mechanism includes a linking rod mounted to the stationary seat and a blind unit wound on the linking rod. The coupling mechanism includes a transmission unit connected to the linking rod and movable between an operable state and a non-operable state, a stop unit for restraining rotation of the linking rod when the transmission unit is at the non-operable state, and a resilient member for biasing the transmission unit toward the non-operable state. The control pole is connected to the transmission unit and is operable for converting the transmission unit to the operable state against a resilient force of the resilient member.