A roller blind, comprising: a linkage assembly, including an outer tube connected with a curtain fabric; and a control device, disposed at one end of the outer tube and engaged with the outer tube, the control device comprising: a reeling mechanism, having an engaging portion; a solenoid valve, disposed in the reeling mechanism; a push mechanism, movably disposed on the reeling mechanism, the push mechanism being connected with the solenoid valve; a front cap, engaged with the engaging portion of the reeling mechanism, the front cap being connected with the push mechanism; and a damper; wherein after the solenoid valve is energized, the solenoid valve drives the push mechanism to push against the front cap so as to separate the front cap from the engaging portion, and the reeling mechanism is not subject to a resistance of the damper to drive the outer tube to rotate so as to lower the curtain fabric; wherein the reeling mechanism includes a reeling wheel,, characterized in that said damper is disposed in the reeling mechanism and in that said reeling mechanism further includes an inner cylinder and an outer cylinder, the reeling wheel has an action portion connected to the inner cylinder, the engaging portion includes a first engaging portion disposed on the inner cylinder and a second engaging portion disposed on the outer cylinder, the inner cylinder and the outer cylinder are detachably engaged with the front cap through the first engaging portion and the second engaging portion. a linkage assembly, including an outer tube connected with a curtain fabric; and a control device, disposed at one end of the outer tube and engaged with the outer tube, the control device comprising: a reeling mechanism, having an engaging portion; a solenoid valve, disposed in the reeling mechanism; a push mechanism, movably disposed on the reeling mechanism, the push mechanism being connected with the solenoid valve; a front cap, engaged with the engaging portion of the reeling mechanism, the front cap being connected with the push mechanism; and a damper; wherein after the solenoid valve is energized, the solenoid valve drives the push mechanism to push against the front cap so as to separate the front cap from the engaging portion, and the reeling mechanism is not subject to a resistance of the damper to drive the outer tube to rotate so as to lower the curtain fabric; wherein the reeling mechanism includes a reeling wheel,, characterized in that said damper is disposed in the reeling mechanism and in that said reeling mechanism further includes an inner cylinder and an outer cylinder, the reeling wheel has an action portion connected to the inner cylinder, the engaging portion includes a first engaging portion disposed on the inner cylinder and a second engaging portion disposed on the outer cylinder, the inner cylinder and the outer cylinder are detachably engaged with the front cap through the first engaging portion and the second engaging portion. a reeling mechanism, having an engaging portion; a solenoid valve, disposed in the reeling mechanism; a push mechanism, movably disposed on the reeling mechanism, the push mechanism being connected with the solenoid valve; a front cap, engaged with the engaging portion of the reeling mechanism, the front cap being connected with the push mechanism; and a damper; wherein after the solenoid valve is energized, the solenoid valve drives the push mechanism to push against the front cap so as to separate the front cap from the engaging portion, and the reeling mechanism is not subject to a resistance of the damper to drive the outer tube to rotate so as to lower the curtain fabric; wherein the reeling mechanism includes a reeling wheel,, characterized in that said damper is disposed in the reeling mechanism and in that said reeling mechanism further includes an inner cylinder and an outer cylinder, the reeling wheel has an action portion connected to the inner cylinder, the engaging portion includes a first engaging portion disposed on the inner cylinder and a second engaging portion disposed on the outer cylinder, the inner cylinder and the outer cylinder are detachably engaged with the front cap through the first engaging portion and the second engaging portion.