PURPOSE: To restrain upper and lower housings so that they are not moved in the transporting direction of slab by moving pistons on the inlet side of slab by supplying fluid pressure to fluid pressure chambers and bringing the piston into contact with edger housing liners.

CONSTITUTION: The pistons 60, 61 are moved on the inlet side (A side) of slab by supplying fluid pressure from fluid pressure source to the fluid pressure chambers 62, 63 in upper and lower roll chocks 14, 15 and slide liners 74, 75 are pressed against the edger housing liners 12a, 13a. The upper and lower roll chocks 14, 15 are pushed out on the outlet side (B side) of slab and the upper and lower roll chocks 14, 15 are restrained so as not to move in the transporting direction by press-fixing roll chock liners 18b, 19b to the edger housing liners 12b, 13b.