PURPOSE: To pass smoothly a passing body by moving cleaning machine onto swinging rails provided on the extension of both ends of fixed rails, and retreating the cleaning machine in the state moved thereto only in passage of the passing body.

CONSTITUTION: Rectangular swinging rails 21 are provided on the extension of both ends of fixed rails 2, and one end of the swinging rails 21 on the side of the fixed rails 2 is supported rotatably by a supporting shaft 22 and made swingable in the horizontal direction. Only when a cleaning machine 3 is located at the terminal of the swinging rails 21, the swinging rails 21 are retreated in the direction opposite to the side of a path where a passing body 7 passes.