Structure of button switch: the button is generally composed of button cap, return spring, bridge moving contact, static contact, pillar connecting rod and shell. When the button is not affected by external force (i.e. static state), the opening and closing state of the contact is divided into start button (i.e. normally open button), stop button (i.e. normally closed button) and composite button (i.e. button with normally open and normally closed contacts integrated). For the start button, the contact will close when the button cap is pressed, and the contact will be automatically disconnected and reset after release; on the contrary, when the button cap is pressed, the contact will be separated, and the contact will be closed and reset automatically after release. When the button cap is pressed down, the bridge moving contact moves downward, so that the normally closed contact is first disconnected, and then the normally open contact is closed; when the button cap is released, the normally open contact is first broken and reset, and then the normally open contact is closed and reset.