To provide a dustproof mechanism having high dustproof effects and capable of responding to a plurality of arm parts.

The dustproof mechanism is provided with a support member 4 supporting the arm parts mounted with a substrate, connected to a guide mechanism 22 provided within a support column 9 via a linear opening part provided on the outer face of the support column 9, and moving an opening of the opening part following the guide mechanism 22, and with a seal belt 5b for sealing the opening part to isolate inside of the support column 9 from outside. Even when the support member 4 is moved by the guide mechanism 22, the seal belt 5b prevents inside of the support column 9 from being exposed to outside. Both ends of the seal belt 5b are fixed to inside of the support column 9, and the seat belt 5b is wound around rollers 35-42 rotatably supported by the support member 4 and installed to seal the opening part.