PURPOSE: To increase the speed of a rolling roll of the upstream side, even if the rolling reduction of area is changed.

CONSTITUTION: The speed change gear is provided with a first driving shaft 12 which is manufactured in a driving motor 7, and also, connected to a rolling roll 16 of a first rolling mill, a first gear 19 inserted and fitted so as to be freely rotatable into a first driving shaft concerned 12, a second driving shaft 21 which is placed coaxially with said first driving shaft 12, and also, connected to a rolling roll 24 of a second rolling mill, a second gear 26 which is provided so as to be unrotatable against a second driving shaft concerned 21 and whose number of teeth is different from that of said first gear 19, a transfer mechanism 32 which is engaged to both of a second gear concerned 26 and said first gear 19, changes a speed of a rotation of a first driving shaft 12 and can transfer it to a second driving shaft 21, and a clutch mechanism 33 which can engage selectively said first driving shaft 12 to said first gear 19 or said second driving shaft 21.