A cord-winding device for a Venetian blind includes: a first reel; a driving unit including a driving wheel and a spring-winding wheel; and a brake unit including a driven gear, a driving member, a ratchet wheel sleeved on the driving member, a plurality of friction members disposed between the driving member and the ratchet wheel, and at least pawl biased to engage the ratchet wheel. When the driven gear is driven by the first reel to rotate in a direction, rotation of the ratchet wheel is stopped by the pawl so that the driving member drives the friction members to rotate, and when the driven gear is driven by the driving wheel to rotate in an opposite direction, the driving member drives rotation of the friction members and, thus, the ratchet wheel.