To automatically mount by a machine a sheet material called 'sign board' for displaying identification information about articles stacked on a pallet.

In a sheet material inserting device for a palletizer, a holding means 5 for holding the sheet material 4 displaying the information about the articles 3 is supported by a transporting means 12 reciprocating from a supply position for supplying the sheet material 4 to an insert position for overlapping part of the sheet material 4 on the articles 3 stacked by the palletizer. The holding means 5 and the transporting means 12 are provided with a controlling means 55 for performing driving control where the holding means 5 holds the sheet material 4 and the sheet material 4 is transported to the insert position by the transporting means 12 and separated after the completion of a first stacking process in which the palletizer for sequentially stacking a predetermined number of articles 3 stacks the articles 3 until the midway.