A cord safety device for a window covering includes a first and a second body. The first body includes: a first pivot portion, disposed on a periphery; a first fixing portion, disposed on a periphery at a predetermined angle with respect to the first pivot portion; a first stop portion, disposed on an inner side of the first body and protruded towards the second body; a first recess, disposed on an upper periphery; and a guiding block, disposed on one end of the first stop portion adjacent to the first fixing portion, in which the guiding block has a guiding surface for guiding the cords. The second body includes: a second pivot portion, disposed corresponding to the first pivot portion; and a second fixing portion, disposed corresponding to the first fixing portion, thereby being separably fixed with the first fixing portion.