Transfer material carrying controlling apparatus

In a multiplex transfer system image generating device, a transfer material carrying device 14 has a main carrying roll 31 for carrying a transfer material S to a transfer material holder 15, a subsidiary carrying roll 32 for transferring the transfer material to the main carrying roll 31 to generate a loop L, a transfer material detecting sensor 35 provided close to the main carrying roll 31, and a jam judging timer for judging the jam of the transfer material S on the basis of a detection signal of the transfer material detecting sensor 35. The driving timing of the main carrying roll 31 is controlled by a rotation position reference signal of the transfer material holder 15. In the case of adjusting timing to drive the main carrying roll 31, the judging time for the jam judging timer and the timing to drive the subsidiary carrying roll 32 are changed in accordance with the adjusted timing, so as to ensure the optimum quantity of the loop of the transfer material S.