A safety device with two conveying systems in the sheet feeder of a machine, capable of processing a sheet-shaped material. An objective of the invention is to construct a generic sheet feeder for large-format machines so that only stacks with a specified maximum weight can reach the processing stage. The present invention encompasses a weighing device (22, 28) located in the sheet feeder (1), which determines the weight of the stack (4), is positioned on the stack carrier (3) and is connected with a regulating and controlling device (19) controlling the driving mechanism (8). At least one permissible total weight is stored in the regulating and controlling device (19). The regulating and controlling device (19) compares the weight of the stack with said stored permissible total weight and the driving mechanism (8) is activated only if the weight of the stack does not exceed the permissible total weight.