A circuit protecting device somprises mainly a housing, an insulation piece, a bimetallic blade, a spring and a press button. The housing has a cover and a main body provided with two partition blocks forming a spring slot and a press button slot communicating with the spring slot. The bimetallic blade has an end fastened to one of two terminals and has another end provided with a contact piece in contact with another one of the two terminals. The spring embracing the outer end of the insulation piece is received in the spring slot of the main body of the housing while the press button is received in the press button slot of the main body of the housing. The inner end of the press button is provided with an insertion hole for receiving therein the outer end of the insulation piece. When a current overload takes place, the heat so generated causes the bimetallic blade to deform so as to force the press button to move outwards until two restrictive flanges of the press button are obstructed by two arresting portions located at the port of the press button slot of the main body of the housing.