The stacker comprises a pair of protrusions 6 prominent from side walls 5 in a spaced relation to each other to form a second opening 7 between protrusions 6, an interim chamber 13 defined by partitions 3 and protrusions 6, and a pair of inner surfaces 8 formed on protrusions 6 prominent into interim chamber 13 from side walls 5 more inward than side surfaces of a holding chamber 12. Largely deviated one of side edges of document D comes into contact to inner surface 8 in interim chamber 13 to push document D inward by projection of inner surface 8 to store document D in a vault 30 with the tolerable deviation upon stowage of a subsequent document D.