An actuating mechanism for moving a highly movable flap of a piece of furniture includes a main body intended for attachment to a furniture body. An actuating arm for moving the flap has one end mounted on a bearing axis of the main body and the other end mounted on a bearing axis of a fitting part intended for attachment to the flap. An additional control arm for moving the flap is also provided. During the movement of the control arm, the effective lever arm length of the control arm can be varied, and the effective lever arm length of the control arm is shortened when opening the actuating arm.