A lower surface cooling box 12 is arranged between transfer rolls 11 on a runout table 3 and an upper cooling box 14 moving freely is arranged at a position corresponding to the cooling box 12 to eject cooling water to the steel strip symmetrically in the vertical direction. The steel strip passes the center of converge of cooling water from upper and lower surfaces of the steel strip. A water breaking roll 16 is provided elevating freely at least at the outlet side rotating at the same peripheral speed as the transfer rolls and is rotated to lower concurrently with passing of the steel strip top at the cooling apparatus. The upper cooling box is also lowered concurrently to cool the steel strip.