A switch structure comprises a control element, which comprises an alloy piece and a swing contact device. The alloy piece includes an actuating piece with a convex part, which has a upper side normally pushing the lower surface of the end part in the swing contact device so that the actuating piece ejects outwards and escapes from the end part when the alloy piece is overheated because of the current flowing through therein overloaded. Therefore, the end part falls down due to no support force and the head part of the swing contact device deforms upwards and does not press on the elastic contact piece. The elastic contact piece is released from the pressing of the swing contact device to eject upwards. Two joints connected in an electric loop are tripped. The object of rapid response, cutting power source, and safety is therefore achieved.