A displacement detector, comprising: an arm (11, 21) supported rotatably at a fulcrum (13, 23) of rotation; first and second contacts (12A,B, 22A,B) extending substantially 180 degrees in different directions from one end of the arm (11, 21); first and second movable detection elements (25A,B) provided so that they extend substantially 180 degrees in different directions from the other end of the arm and move on an arc with the fulcrum of rotation as its center in accordance with the rotation of the arm first and second fixed detection elements (26A,B) provided so that the respective relative positional relationships change in accordance with the movement of the first and second movable detection elements (25A,B); a detection section that generates, when the first and second movable detection elements (25A,B) are within predetermined positional relationship ranges with respect to the first and second fixed detection elements (26A,B), respectively, detection signals in accordance with the respective positional relationships; and an arm biasing means for biasing the arm so that it rotates toward a reference rotation position, the means biasing the arm in the opposite direction in accordance with the direction of rotation from the reference rotation position, wherein: when the arm rotates toward one side from the reference rotation position, the first movable detection element is within the predetermined positional relationship range with respect to the first fixed detection element and the detection section generates a detection signal in accordance with the positional relationship of the first movable detection element with respect to the first fixed detection element; and when the arm rotates toward the other side from the reference rotation position, the second movable detection element is within the predetermined positional relationship range with respect to the second fixed detection element and the detection section generates a detection signal in accordance with the positional relationship of the second movable detection element with respect to the second fixed detection element. an arm (11, 21) supported rotatably at a fulcrum (13, 23) of rotation; first and second contacts (12A,B, 22A,B) extending substantially 180 degrees in different directions from one end of the arm (11, 21); first and second movable detection elements (25A,B) provided so that they extend substantially 180 degrees in different directions from the other end of the arm and move on an arc with the fulcrum of rotation as its center in accordance with the rotation of the arm first and second fixed detection elements (26A,B) provided so that the respective relative positional relationships change in accordance with the movement of the first and second movable detection elements (25A,B); a detection section that generates, when the first and second movable detection elements (25A,B) are within predetermined positional relationship ranges with respect to the first and second fixed detection elements (26A,B), respectively, detection signals in accordance with the respective positional relationships; and an arm biasing means for biasing the arm so that it rotates toward a reference rotation position, the means biasing the arm in the opposite direction in accordance with the direction of rotation from the reference rotation position, wherein: when the arm rotates toward one side from the reference rotation position, the first movable detection element is within the predetermined positional relationship range with respect to the first fixed detection element and the detection section generates a detection signal in accordance with the positional relationship of the first movable detection element with respect to the first fixed detection element; and when the arm rotates toward the other side from the reference rotation position, the second movable detection element is within the predetermined positional relationship range with respect to the second fixed detection element and the detection section generates a detection signal in accordance with the positional relationship of the second movable detection element with respect to the second fixed detection element. when the arm rotates toward one side from the reference rotation position, the first movable detection element is within the predetermined positional relationship range with respect to the first fixed detection element and the detection section generates a detection signal in accordance with the positional relationship of the first movable detection element with respect to the first fixed detection element; and when the arm rotates toward the other side from the reference rotation position, the second movable detection element is within the predetermined positional relationship range with respect to the second fixed detection element and the detection section generates a detection signal in accordance with the positional relationship of the second movable detection element with respect to the second fixed detection element.