A wire-driving device for a window regulator comprising a worm wheel rotatably contained in a housing, first and second pulleys arranged at both sides of the worm wheel respectively, means for transmitting torque from worm wheel to the pulleys and a worm meshing with the worm wheel and being driven by a motor, whereby first and second wires wound round the pulleys respectively are driven. The motor driven wire-driving device is thinner than conventional devices.