PURPOSE: To obtain a casting slab having a good characteristic while preventing surfase transverse cracking and bulging by controlling the solidified shells forming on the drum surfaces of a twin-drum type continuous casting machine for a thin sheet in a way as to satisfy inequality I , II.

CONSTITUTION: A molten metal is poured into the space formed of two water cooled casting rolls 1, 1' and two stationary gates and the solidified shells formed on cooling are united to a casting slab 3. If the matching point P of two sheets of the solidified shells exists on the neutral point of the rolls 1, 1', the point P is so controlled as to satisfy the equation I . In the equation, l denotes the distance mm from the neutral point P of the rolls 1, 1', (t) denotes the thickness mm of the slab 3 and R denotes the radius mm of the rolls 1, 1'. If the point P of two sheets of the solidified shells is lower than the neutral point of the rolls 1, 1', the point P is so controlled as to satisfy the equation II. In the inequality, m denotes the width mm in the unsolidified part on the neutral point line of the rolls, (t) denotes the thickness mm of the slab 3 and (h) denotes the head mm of the molten metal.