To provide a diagnostic method for operation of abnormality in the rolling line which enables one to specify immediately which operational abnormality is being caused among a slip of metal rolling, a slip of rolls in delivery line, an abnormality of a thickness scale, and a foreign material rolling.

Operational abnormalities can be specified by a combination of such three checks as a result of coil weight check before a metal rolling which enables one to judge if a foreign material rolling has been conducted or not, a calculated coil weight check which compares calculated coil weights with actually measured coil weights by a scale and a result of wrapping check.