A wire-winding device comprising: an upper cover; a spiral spring; a rotary base having a groove to accommodate the spiral spring on the bottom surface thereof; a transmission line winding around the rotary base; a lower cover assembled with the upper cover; and a pillar, an outlet, and a wire casing formed on one side of the groove, and two spacers surrounding the peripheral edge of the groove, the pillar having a first end portion which shifts outward to the edge of rotary base, the wire casing having a smooth curved surface formed on the bottom surface thereof near the outlet to enlarge the accommodating space near the outlet and reduce the friction between the transmission line and the spacers.