To provide a power transmission device with which the driving of ranged roll stands is enabled by a simple composition and at different velocity ratios in a continuous rolling mill.

The continuous roll stands 10, 12 in the mill are connected to a pair of drive shafts 22 arranged in parallel. An idler shaft 24 is arranged in parallel to the drive shafts 22. On the respective of a pair of drive shafts 22, a 1st drive gears G1, G2 and 2nd drive gears G4, G5 are rotatably arranged. On the idler shaft 24, an idler gear G3 which forms a 1st drive train together with a 1st drive gears G1, G2 and idler gear G6 which forms the 2nd drive train together with the 2nd drive gears G4, G5 are fixedly arranged. With a clutch 34, the drive gears G1-G5 of the 1st and 2nd drive trains are operated so as to selectively connect to the respective drive shafts 22.