An ON/OFF detecting buckle switch includes: a case in a housing shape; a substrate fixing member equipped in an inner side face of the case; a slider insertion port equipped in an upper face of the case; a support portion equipped in an inner side face of the case; a first fixed terminal folded stepwise in a longitudinal direction of a strip shape to circumvent the substrate fixing member, having one end provided with a notched portion and the other end fixed to the inner side face of the case; a first movable terminal in a strip shape having one area fixed to the support portion; a slider provided with a terminal press portion that projects inside the case penetrating through the slider insertion port and the notched portion, and when pressed down, presses down an end of the first movable terminal; and a spring that biases the slider upward.