A slider moving in a sliding direction between first and second positions shifts a second path-defining member, relative to a first path-defining member, between first and second states. A pair of movable members each disposed on a corresponding side of a slider in a width direction is movable individually in the sliding direction to shift between third and fourth states. The movable members, when both in the third state, position the slider to the first position and, when both in the fourth state, position the slider to the second position. Each movable member supports a corresponding widthwise end of the slider immovably in the sliding direction and movably in the width direction. A support frame supporting the second path-defining member supports a widthwise central portion of the slider movably in the sliding direction and rotatably on a plane parallel to the sliding direction and the width direction.