The present invention relates to a method for identifying a defect occurrence source, said method including identifying a roll that generates defects at constant intervals in a conveying direction of a sheet-shaped glass when the sheet-shaped glass is conveyed by a plurality of rolls in an annealing device including a conveying device having the plurality of rolls, in which a peripheral velocity of a certain roll of the plurality of rolls is changed so as to be different from a conveyance speed of the sheet-shaped glass, thereby identifying a roll constituting the defect occurrence source, according to the result of a determination on whether or not there has been a change in intervals between the defects before and after changing the peripheral velocity.