A bank quantity adjusting device for an extruder capable of accurately controlling a bank quantity regardless of a difference in composition of a material to be extruded. The bank quantity adjusting device includes a pressure sensor 13 for detecting a bank pressure between an outlet 7 of an extruder body 1 provided with material extruding screws 3 and a roller die 2 provided before the outlet 7, and a control device 15 for controlling one or both of a screw speed and a roller die speed according to a difference between the bank pressure detected by the pressure sensor 13 and a set target pressure. The bank quantity adjusting device further includes bank quantity detector 14 for detecting a bank quantity between the outlet 7 and the roller die 2, and a processor 16 provided in the control device 15 for obtaining a correlation between the bank quantity and the bank pressure from a detection value of the bank quantity detected by the bank quantity detector 14 and a detection value of the bank pressure detected by the pressure sensor 13 upon detection of the bank quantity, converting a target value of the bank quantity into a pressure value by using the correlation obtained above, and setting this pressure value to the above target pressure.