Guide-rail brake

A guide-rail brake of an elevator and a method for controlling the brake are provided. The brake comprises a frame part fixed to the elevator car, a prong part, which contains turning jaws that correspond to the guide rail via the braking surfaces when braking, a spring loading the prong part to press the braking surfaces to the guide rail, and a controllable mover, which is an electromagnet, which contains two pulling core pieces. The force effect of the electromagnet on the prong part is opposed to the spring. In the guide-rail brake an air gap (ag) is structurally arranged between the center parts of the pulling core pieces of the electromagnet of the guide-rail brake when the brake is fully energized, and a damping circuit is arranged in the coil of the electromagnet of the guide-rail brake to speed up operation of the guide-rail brake.