Sliding nozzle device

1 . A sliding nozzle device comprising: a fixed metal frame; and a sliding metal frame slidably provided to the fixed metal frame,

wherein the fixed metal frame is provided with a mark block so that a maintenance robot can recognize a position of the mark block, the mark block being provided to protrude from a side surface or bottom surface of the fixed metal frame toward the sliding metal frame, at a position free from interference with the sliding metal frame during sliding,

wherein a laser irradiator of the maintenance robot irradiates the mark block with laser light and a camera of the maintenance robot takes an image of the laser light irradiating the mark block so as to recognize the position of the fixed metal frame.

2 . The sliding nozzle device as claimed in claim 1 , which is configured to during use, slide the sliding metal frame within a first sliding range under a condition that a surface pressure is loaded between the fixed metal frame and the sliding metal frame, and during maintenance, slide the sliding metal frame to an outside of the first sliding range, thereby unloading the surface pressure, wherein the mark block is positioned such that it is covered by the sliding metal frame or a shielding plate provided to the sliding metal frame, when the sliding metal frame is slid within the first sliding range, but not covered by the sliding metal frame or the shielding plate, when the sliding metal frame is slid to the outside of the first sliding range.