To improve sealing performance by forming a labyrinth-like seal gap between each guide rail and each seal rail.

The device 21 for opening and closing an opening 2a of a heating furnace 2 by a screen door 31 is provided with a driving mechanism 71 moving the screen door 31 along the opening 2a, an opening and closing casing 50 housing the screen door 31 in a closed position, a plurality of guide rails 62 protruding from the opening and closing casing 50 along the screen door 31, and a plurality of seal rails 32 protruding from the screen door 31 to engage with each guide rail 62. The heating furnace 2 is sealed by engagement parts of each guide rail 62 and each seal rail 32.