A Without working floor which is installed inside the tubular structure is reliably inclined, and to provide a movable working floor system does not interfere with the work. For A vertical tubular structure 1 of the inner surface of inspection and maintenance the movable working floor device 20 having a vertically movable working floor which is installed inside the tubular structure, the tubular structure a working floor 21 that is disposed therein, a plurality of rope winding device 25 provided on at least three positions of the working bed, than the ceiling portion 11A of the tubular structure outside of the tubular structure be attached to the hanging steel structure 60 located above a pulley 61 located above each rope winding device, it bridged between the rope winding device and the pulley corresponding thereto a rope 62, a tilt detection device for detecting an inclination of the working floor, with adjusting the inclination of the working floor receiving the inclination signal from the inclination detecting unit, to allow changing the height of the working floor, a plurality and a control unit 30 for controlling the rope winding device. .The